feat(testing): Laravel-style fluent JSON assertions

[bedus-creation]

Summary

Adds a Laravel AssertableJson-style fluent assertion API for HTTP tests (TASK #107). HTTP test responses are now chainable and scope-aware.

response.assert_ok().assert_json(lambda json: (
    json.where("id", 1)
        .where("name", "Bedu")
        .where("active", lambda v: v is True)
        .has("profile", lambda p: p.where("email", "a@b.com").etc())
        .etc()
))

What's included

• AssertableJson (fastapi/testing/assertable_json.py)
  • Matching: where, where_not, where_all, where_type (incl. "string|null" unions; bool is not integer)
  • Presence: has, has_all, has_any, missing, missing_all, count
  • has(key, callback) / has(key, length, callback) nested scoping
  • Traversal: first, each
  • Strict interaction model (_verify): un-asserted object keys fail unless .etc() is called — catches unexpected/leaked response keys
  • Dotted-key paths and callable predicate matchers; errors include the full key path
  • Phase-2 methods (where_contains, count_between, where_all_type) stubbed with NotImplementedError
• TestResponse (fastapi/testing/test_response.py): thin httpx.Response wrapper adding assert_status, assert_ok, assert_created, assert_no_content, assert_json (incl. exact=). __getattr__ passthrough keeps existing tests green.
• HttpTestCase get/post/put/patch/delete now return TestResponse.

Tests

• New unit tests: happy path, predicate matcher, where_type, nested scoping, first/each, etc(), strict un-asserted-prop failure, TestResponse helpers (40 tests).
• Full suite green: 1493 passed, 7 skipped. Ruff clean.

🤖 Generated with Claude Code