Add missing PromptBuilder convenience wrappers to control media output

[felixarntz]

The PromptBuilder was missing methods to control 3 ModelConfig properties:

• outputMediaOrientation
• outputMediaAspectRatio
• outputSpeechVoice

Additionally, this PR fixes an odd but somewhat important bug with the usingStopSequences method not working at all (it needs to set the top-level key, not a key in customOptions).

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.48%. Comparing base (30a1506) to head (1134643).
⚠️ Report is 7 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #218      +/-   ##
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+ Coverage     87.45%   87.48%   +0.02%     
- Complexity     1194     1197       +3     
============================================
  Files            60       60              
  Lines          3858     3867       +9     
============================================
+ Hits           3374     3383       +9     
  Misses          484      484              

Flag	Coverage Δ
unit	87.48% <100.00%> (+0.02%)	⬆️

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[felixarntz]

@JasonTheAdams One other thing to consider here is that we also don't support setting custom options via PromptBuilder convenience methods - they can only be set by using the slightly more complex usingModelConfig method.

Maybe that's still a reasonable path forward, because using those is more advanced and assumes extra responsibility on the caller - they will need to know whether the API supports a specific custom option or not - but I wanted to bring it up so we can consider whether or not to add a convenience method for them.

If we want to include that in the PromptBuilder, it could be a simple PromptBuilder::usingCustomOption(string $option, $value).

[gziolo]

Code review looks good. All checks pass locally (tests, PHPCS clean, PHPStan clean). The stop sequences bug fix is important and the new convenience methods follow established patterns consistently. The changes are straighforwad and covered properly with tests.

Re: custom options convenience method — agree it's worth considering as a follow-up, but shouldn't block this PR.