Revisit use of comma-separated lists

[juruen]

Context

In #18 and other PRs where parameters can be expressed through arrays, we are using comma-separated lists instead as they seemed to cause issues in the clients.

As things are moving quite fast, let's revisit its use.

[juruen]

The issue was related to the array schemas not being compliant. This has been resolved, and we already have a couple of tools using arrays.

We can now migrate the existing comma-separated lists at our earliest convenience.

[williammartin]

Here are the places this is an issue:

conformance_test.go:254:
                Error Trace:    /Users/williammartin/workspace/github-mcp-server/conformance/conformance_test.go:254
                Error:          Received unexpected error:
                                inputSchema mismatch for tool "create_issue":
                                  conformance_test.inputSchema{
                                        Type: "object",
                                        Properties: map[string]any{
                                                "assignees": map[string]any{
                                                        ... // 1 ignored entry
                                -                       "items": map[string]any{"type": string("string")},
                                -                       "type":  string("array"),
                                +                       "type":  string("string"),
                                                },
                                                "body": map[string]any{"type": string("string"), ...},
                                                "labels": map[string]any{
                                                        ... // 1 ignored entry
                                -                       "items": map[string]any{"type": string("string")},
                                -                       "type":  string("array"),
                                +                       "type":  string("string"),
                                                },
                                -               "milestone": map[string]any{"description": string("Milestone number to assign"), "type": string("number")},
                                                "owner":     map[string]any{"type": string("string"), ...},
                                                "repo":      map[string]any{"type": string("string"), ...},
                                                "title":     map[string]any{"type": string("string"), ...},
                                        },
                                        Required: {"owner", "repo", "title"},
                                  }

                                inputSchema mismatch for tool "list_issues":
                                  conformance_test.inputSchema{
                                        Type: "object",
                                        Properties: map[string]any{
                                                "direction": map[string]any{"enum": []any{string("asc"), string("desc")}, "type": string("string"), ...},
                                                "labels": map[string]any{
                                                        ... // 1 ignored entry
                                -                       "items": map[string]any{"type": string("string")},
                                -                       "type":  string("array"),
                                +                       "type":  string("string"),
                                                },
                                                "owner": map[string]any{"type": string("string"), ...},
                                                "page":  map[string]any{"type": string("number"), ...},
                                                ... // 5 identical entries
                                        },
                                        Required: {"owner", "repo"},
                                  }

                                inputSchema mismatch for tool "update_issue":
                                  conformance_test.inputSchema{
                                        Type: "object",
                                        Properties: map[string]any{
                                                "assignees": map[string]any{
                                                        ... // 1 ignored entry
                                -                       "items": map[string]any{"type": string("string")},
                                -                       "type":  string("array"),
                                +                       "type":  string("string"),
                                                },
                                                "body":         map[string]any{"type": string("string"), ...},
                                                "issue_number": map[string]any{"type": string("number"), ...},
                                                "labels": map[string]any{
                                                        ... // 1 ignored entry
                                -                       "items": map[string]any{"type": string("string")},
                                -                       "type":  string("array"),
                                +                       "type":  string("string"),
                                                },
                                                "milestone": map[string]any{"type": string("number"), ...},
                                                "owner":     map[string]any{"type": string("string"), ...},
                                                ... // 3 identical entries
                                        },
                                        Required: {"owner", "repo", "issue_number"},
                                  }