feat: Add ULID generation and manipulation support

[muminoff]

Summary

Adds comprehensive ULID (Universally Unique Lexicographically Sortable Identifier) generation and manipulation tool to ut.

Features

• ✅ Generate single or multiple ULIDs with --count flag
• ✅ Parse ULIDs to extract timestamp, datetime, and bytes
• ✅ Validate ULID strings
• ✅ Convert between ULID and UUID formats (bidirectional)

Technical Details

• Uses ulid crate v1.2.1 with serde and uuid features
• Includes 8 comprehensive unit tests (all passing)
• Follows existing tool patterns (similar to UUID and URL tools)
• Returns JSON output for easy integration
• Zero compilation warnings

Usage Examples

ut ulid                    # Generate 1 ULID
ut ulid -c 5               # Generate 5 ULIDs
ut ulid parse <ulid>       # Show timestamp and details
ut ulid validate <ulid>    # Check if valid
ut ulid to-uuid <ulid>     # Convert to UUID
ut ulid from-uuid <uuid>   # Convert from UUID

Test Results

All 8 unit tests passing:

• test_generate_single
• test_generate_multiple
• test_validate_valid
• test_validate_invalid
• test_parse
• test_ulid_to_uuid_conversion
• test_uuid_to_ulid_conversion
• test_roundtrip_ulid_uuid_ulid