llms/openai: rename function call tests to clarify deprecated vs recommended API

[karsharma10]

Summary

• Rename TestFunctionCall → TestFunctionCallDeprecated to clarify it tests the deprecated WithFunctions API
• Add new TestFunctionCall test that uses the recommended WithTools API
• Add httprr recording for the new test

Context

The WithFunctions option is deprecated in favor of WithTools. This change makes it explicit which test covers the deprecated API (for backward compatibility) and adds proper test coverage for the recommended API.

Recording

The httprr file was generated with:

cd llms/openai && go test -v -httprecord=. -run "TestFunctionCall$"

PR Checklist

• Read the Contributing documentation.
• Read the Code of conduct documentation.
• Name your Pull Request title clearly, concisely, and prefixed with the name of the primarily affected package you changed according to Good commit messages (such as memory: add interfaces for X, Y or util: add whizzbang helpers).
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. Fixes #123).
• Describes the source of new concepts.
• References existing implementations as appropriate.
• Contains test coverage for new functions.
• Passes all golangci-lint checks.