refactor: unify timezone parameter naming across Python and JS wrappers

- Rename timezone_id → timezone in launch_context(), launch_persistent_context(),
  and launch_persistent_context_async() (Python)
- Extract _migrate_timezone_id() helper for deprecation compat (DRY)
- Always pop timezone_id from kwargs to prevent override via context_kwargs.update()
- Use FutureWarning (visible by default) instead of DeprecationWarning
- JS: deprecate timezoneId on LaunchContextOptions with runtime shim
- Extract migrateTimezoneId<T>() shared helper in playwright.ts (DRY)
- Bump version to 0.3.7 in _version.py and package.json
- Add 4 Python + 4 JS unit tests for deprecation compat behavior

js/src/types.ts

@@ -33,7 +33,7 @@ export interface LaunchContextOptions extends LaunchOptions {
   viewport?: { width: number; height: number };
   /** Browser locale, e.g. "en-US". */
   locale?: string;
-  /** Timezone, e.g. "America/New_York". */
+  /** @deprecated Use `timezone` (inherited from LaunchOptions) instead. */
   timezoneId?: string;
   /** Color scheme preference — 'light', 'dark', or 'no-preference'. */
   colorScheme?: "light" | "dark" | "no-preference";