fix(zod-openapi): inherit defaultHook from parent app on nested routes

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Closes #1306.

When mounting a nested OpenAPIHono via app.route(path, subApp), the sub-app's routes did not pick up the parent's defaultHook. The default hook on the parent was only applied to routes registered directly on the parent (PR #408 did the analogous fix for basePath()).

The validator's hook parameter defaulted to this.defaultHook at registration time, so sub-app routes registered before mounting were bound to undefined. Switched the default to a lazy wrapper that reads this.defaultHook at request time, and propagated the parent's defaultHook to the sub-app on route() when the sub-app does not declare its own.

Added a regression test under the Routers describe block that fails on main and passes with the fix.

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🦋 Changeset detected

Latest commit: fe3858b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@hono/zod-openapi	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.01%. Comparing base (95c2039) to head (fe3858b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1878      +/-   ##
==========================================
+ Coverage   92.00%   92.01%   +0.01%     
==========================================
  Files         115      115              
  Lines        3925     3930       +5     
  Branches     1005     1009       +4     
==========================================
+ Hits         3611     3616       +5     
  Misses        282      282              
  Partials       32       32              

Flag	Coverage Δ
zod-openapi	95.06% <100.00%> (+0.15%)	⬆️

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