PHP NextGen: address PSR-12 formatting violations

[gcatanese]

This pull request refactors the ObjectSerializer Mustache template to avoid generating code that is not aligned to PSR-12 guidelines.

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  ./mvnw clean package || exit
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  Commit all changed files.
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@jebentier (2017/07), @dkarlovi (2017/07), @mandrean (2017/08), @jfastnacht (2017/09), @ybelenko (2018/07), @renepardon (2018/12) @wing328

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Summary by cubic

Aligns the PHP NextGen ObjectSerializer template with PSR-12 so generated clients are standards-compliant. Regenerated sample clients to reflect formatting-only changes.

• Refactors
  • PSR-12 style in ObjectSerializer.mustache: spacing for casts/foreach, switch # to // comments, add braces for single-line if, align docblocks.
  • Use "\DateTime" in query param type checks; standardize (object) $values casting in sanitize/deserialize.
  • Regenerate PHP NextGen samples (echo_api and petstore) to match the updated template.

^{Written for commit 5e48b1e. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files