fix: respect backticks when splitting column names in PrepareBatch

[Laotree]

Fixes issue #1827 where PrepareBatch would incorrectly split column names on comma without respecting backticks or double quotes. For example:

INSERT INTO my_table (col1, `my_weird,col2`, col3)

Would incorrectly be parsed as ['col1', 'my_weird', 'col2', 'col3'] instead of ['col1', 'my_weird,col2', 'col3'].

This adds a splitColumnsRespectingQuotes function that properly handles commas inside backtick-quoted and double-quoted column names.

Summary

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added

[github-actions]

Summary

This PR fixes a real parsing bug (#1827) in extractNormalizedInsertQueryAndColumns: the naive strings.Split(columns, ",") broke whenever a column name contained a comma inside backtick or double-quote delimiters (e.g. `my_weird,col2`). The replacement, splitColumnsRespectingQuotes, is a straightforward character-scan that toggles quote-mode on backtick and double-quote boundaries and only splits on commas outside any quoting context. The logic is correct and the approach is idiomatic Go.

Should fix

Missing regression test in tests/issues/.
Per the project's workflow rules, bug fixes require a regression test at tests/issues/issue_1827_test.go. The unit tests added to batch_test.go are a good sanity check for the parsing helper, but they don't exercise PrepareBatch end-to-end against a real ClickHouse instance with a quoted column name containing a comma. Without an integration test, a future refactor of the batch pipeline could silently regress this. A minimal test that creates a table with such a column name, calls PrepareBatch, Appends a row, and Sends would be sufficient.

Nits

• nit: splitColumnsRespectingQuotes doesn't handle escaped/doubled quote characters inside a quoted identifier (e.g. `mycol `` → column literally named `` mycol ``). ClickHouse allows this per the identifier syntax docs. The old strings.Split path didn't handle it either, so this isn't a regression, but it's worth a `// Note: escaped quotes (doubled backtick/double-quote) are not supported` comment on the function so the next reader doesn't wonder.
• nit: The old loop had a comment linking to the ClickHouse identifier syntax docs (// refers to https://clickhouse.com/docs/en/sql-reference/syntax#identifiers). That comment was dropped when the loop was rewritten. Worth keeping it near the strings.ReplaceAll / strings.Trim call so the stripping logic remains self-explanatory.

Verdict

Approve — the fix is correct, the helper function is clean, and the unit tests cover both quoting styles. The missing tests/issues/issue_1827_test.go is the only meaningful gap; please add it before merging to stay consistent with the project's regression test convention.

[Laotree]

The unit test cases have already been added to batch_test.go. Writing separate test cases in issue_1827_test.go would be redundant.