Accept any sequence of header pairs, not just list

[gyanu2507]

We only iterate header pairs. Typing them as list meant a tuple or h11.Headers needed a pointless list(...) copy.

Fixes #173

[gyanu2507]

@Kriechi switched the alias to collections.abc.Sequence in 3330d6d.

[gyanu2507]

@Kriechi switched the alias to collections.abc.Sequence in 3330d6d. Please re-review when you can.

[gyanu2507]

CI is green on tests; the remaining mark is codecov/project coverage. No functional failure on the Sequence-of-headers change.

[gyanu2507]

Pushed Sequence-backed header tests (tuple as well as list) for the list(headers) conversions. GitHub Actions is waiting on maintainer approval for the new run (action_required on the latest CI workflow). Once that runs, Codecov should refresh.

[Kriechi]

Why can't it be the newly defined Headers type with a sequence here and in the similar code changes?

[gyanu2507]

Those two locals are accumulators. We .append header pairs while walking h11's event. Headers is Sequence[tuple[bytes, bytes]], and mypy --strict then reports Sequence[...] has no attribute "append" on those two calls (lines 229 and 420).

Incoming values and extra_headers already use Headers. The handshake still builds a list, then stores it on Request.extra_headers.