chore: improve readability and fix Sonar suggestions in OpenAiChatMod…

[kuntal1461]

Summary

• Refactors OpenAiChatModelMutateTests to enhance readability and maintainability.
• Addresses Sonar warnings (naming, assertions clarity, minor duplication) without changing behavior.

Motivation

• Make the test intent clearer and reduce future review/debug time.
• Keep the codebase aligned with Spring’s quality guidelines and Sonar recommendations.

Changes

• Clarified test names to express “given/when/then” intent.
• Extracted repeated literals into constants.
• Replaced broad assertions with precise, self-describing assertions.
• Removed minor duplication; simplified setup/teardown where safe.
• No production code touched; no functional behavior change.

Testing

• Unit tests updated where needed.

• Local build green:

  ./mvnw -T1C -DskipTests=false clean verify
  # or run just the module:
  ./mvnw -T1C -DskipTests=false -pl models/spring-ai-openai -am clean verify

• Verified the modified tests pass consistently.

Compatibility / Risk

• No API changes, no behavioral changes.
• Scope limited to tests.

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Contributor Checklist (per guide)

• DCO: Commits include Signed-off-by: Your Name <[email protected]> (git commit -s)
• Rebased on latest main and squashed to a single coherent commit
• Added/updated unit tests as needed
• Built locally; all tests pass

[ilayaperumalg]

@kuntal1461 Thanks for the PR cleaning up! LGTM, rebased and merged as fa68d1e

[kuntal1461]

hi @ilayaperumalg Thanks for merging!