Add parse_sql_with_offsets to preserve original source text

[BinaryMuse]

Overview

This PR introduces a new API method Parser::parse_sql_with_offsets() that returns parsed statements along with byte offsets into the original source string.

Motivation

I'm using Parser::parse_sql to parse an arbitrary number of statements. Based on the type of statement, I need to handle execution differently. However, the canonical representation of the Statement includes uppercase type names (in most cases), which don't work as a query for ClickHouse since ClickHouse uses case-sensitive type names: for example, Nullable(Float64) vs Nullable(FLOAT64).

parse_sql_with_offsets returns Vec<(Statement, SourceOffset)>, where SourceOffset::start() and ::end() return the byte offsets of the statement from the original query, allowing me to recover the original source of the statement in question:

let result = Parser::parse_sql_with_offsets(&dialect, &sql).unwrap();
for (statement, offset) in result {
  let original_statement_sql = sql[offset.range()]
}

Alternatives

This seems like it would only be useful while work on #1548 is not yet complete, so it's totally reasonable if you'd prefer this PR not to be merged.

Implementation details

• Add SourceOffset type to track byte positions in source text
• Add Parser::parse_sql_with_offsets() public API method
• Add Parser::parse_statements_with_offsets() internal method
• Add helper function to convert line/column to byte offsets
• Add comprehensive tests covering single/multiple statements and multiline SQL