fix: label timeouts, render empty-but-valid preview bodies, snapshot override dicts (v0.1.4)

- request_with_retries labels an exhausted total-timeout as 'timeout' instead of the
  generic 'unexpected error' catch-all (nit)
- as_curl() renders an empty-but-valid json body ({} / []) via is-not-None instead of
  dropping it as falsy (nit)
- _apply_overwrites snapshots the shared override dicts before iterating, so a
  concurrent mutation can't raise 'dict changed size during iteration' (nit).

Signed-off-by: disqualifier <dev@disqualifier.me>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "aioweb"
-version = "0.1.3"
+version = "0.1.4"
 description = "Async HTTP session wrapper over aiohttp — proxies, header overwrites, retries, previews. Config-free, installable."
 requires-python = ">=3.10"
 dependencies = [