[codex] Use native ClickHouse JSON paths

[ruslandoga]

What changed

• Compile Ecto json_extract_path/2 and bracket JSON access to native ClickHouse JSON subcolumn paths such as json.foo.bar.
• Quote non-identifier JSON keys with backticks in generated native paths.
• Update SQL rendering expectations for JSON path queries.
• Enable the skipped JSON serialization coverage by creating a local settings JSON table in the test and checking native path access.
• Add a JSON integration test for json_extract_path/2 and bracket syntax on nested JSON paths.
• Document the SQL output change as a breaking change in the changelog.

Why

ClickHouse native JSON columns support reading leaf paths as subcolumns, and using JSON_QUERY(json, '$.foo.bar') keeps the adapter on the older function-based path syntax. This changes the adapter to emit the native path form requested by the current JSON support.

Impact

This is a breaking SQL generation change for callers relying on the exact JSON_QUERY(...) output from json_extract_path/2 or Ecto bracket JSON access. Generated queries now use ClickHouse native path syntax.

Related: #269

[ruslandoga]

Released as https://hex.pm/packages/ecto_ch/0.10.0