fix(devtools): support Firefox/Safari stack format in findCallerName (#3469)

* fix(devtools): support Firefox/Safari stack format in findCallerName

The previous regex only matched V8-style frames ("at name (source)").
SpiderMonkey (Firefox) and JavaScriptCore (Safari) use "name@source"
with no spaces, causing the regex to fail and fall back to "anonymous".

Now tries V8 regex first, then Gecko/JSC regex. Regexes extracted to
module-level constants to avoid recompilation on every setState call.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

* fix(devtools): keep findCallerName internal; test Gecko stack via Error stub

- Use function declaration without export so helpers stay private
- Drop redundant || undefined after regex fallback chain
- Replace direct findCallerName import with integration test that stubs
  Error.stack to SpiderMonkey shape and asserts devtools send payload
- Avoids pulling src into old-TypeScript test:types and widening public API

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Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Daishi Kato <dai-shi@users.noreply.github.com>