doc: update context for ngx.req.http_version and ngx.req.raw_header to include log_by_lua

[tzssangglass]

And add test cases to cover.

I hereby granted the copyright of the changes in this pull request
to the authors of this lua-nginx-module project.

[Copilot]

Pull request overview

Updates the documentation and tests to reflect that ngx.req.http_version() and ngx.req.raw_header() are also available in the log_by_lua* context.

Changes:

• Document log_by_lua* as a supported context for ngx.req.http_version and ngx.req.raw_header.
• Add a regression test asserting both APIs work in log_by_lua_block and emit expected log output.
• Update the test plan count to account for the new test’s additional error_log assertions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
t/104-req-raw-header.t	Adds a new log_by_lua test coverage for ngx.req.http_version() and ngx.req.raw_header() and adjusts planned test count accordingly.
README.markdown	Updates API context documentation to include log_by_lua* for ngx.req.http_version and ngx.req.raw_header.

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