[Firebase AI] Fix warnings introduced in #1812

[andrewheard]

• Silenced the Literal value is already handled by previous pattern; consider removing it warnings and added TODOs with context to resolve them in the future.
• Reduced the deployment target to the lowest supported value (17.0 instead of 17.6).
  • Note: This was increased from 15.0 to 17.6 in refactor: Modernize Project Structure and Refine Codebase #1812 since this is the minimum for ConversationKit but the .6 minor version is not needed.
• Fixed a typo that had import ConversationKit within a #if canImport(FirebaseAILogic) but these are unrelated.
  • Will remove the #if canImport(FirebaseAILogic) statements in a follow-up since we depend on Firebase 12.6.0+ where FirebaseAILogic is always available.
• Reverted unintentional copyright year changes on unmodified files in refactor: Modernize Project Structure and Refine Codebase #1812.

To be addressed in a follow-up PR:

• The changes to the firebaseai workflow in refactor: Modernize Project Structure and Refine Codebase #1812 drops all our testing on macos-15.
• The removal of FirebaseAIExampleZip from the Xcode project will likely break the zip workflow in firebase-ios-sdk.
  • Example failing run: https://github.com/firebase/firebase-ios-sdk/actions/runs/19902617427/job/57050431802

[gemini-code-assist]

Code Review

This pull request primarily addresses warnings and minor issues introduced in a previous PR. The changes include silencing compiler warnings about duplicate case patterns by commenting them out and adding TODOs for future resolution, reducing the iOS deployment target, fixing an import statement, and reverting incorrect copyright year updates. The changes are generally good and align with the PR's goal. I've found a minor copy-paste error in a commented-out code block which should be corrected for clarity.

[peterfriese]

Thanks for catching these, @andrewheard !