test: harden recorder test cleanup, dedup helpers, fix assertions

- Clean up previous tmpDir before overwriting in strict mode test
- Replace global fetch with node:http helpers (del, postRaw)
- Wrap default fixturePath test in try/finally for reliable cleanup
- Hoist duplicate createRawUpstream to shared scope
- Add explicit headersSent mock property instead of relying on internals
- Guard setupUpstreamAndRecorder against leaked resources on re-entry
- Narrow bare catch to only swallow expected filesystem errors

Author: jpr5