[theminjunchoi]

What this PR does / why we need it:

Fixes #139

A handler that set details or trailing metadata the front can't take left the call open, so the client waited until its deadline. _answer() now ends the call with INTERNAL on any exception and logs it. If the front already ended the call, this does nothing.

server() also takes what grpc.server() takes here: bytes in set_details() and abort(), and None in set_trailing_metadata(). aio.server() ends a call with bytes details with INTERNAL, since grpc.aio refuses them.

How it was tested:

• New tests check server() and aio.server() with bad details and trailing metadata on unary and stream calls. They fail without this change.
• set_details() with bytes and set_trailing_metadata(None) match grpc.server() on server().
• The full Python test suite passes (272 passed, 3 skipped), run on the 0.8.0 wheel since nothing in Rust changed. ruff passes.

Special notes for your reviewers:

Bad input still gets a different status from grpcio in some cases. For example, abort(code, 5) ends with INTERNAL here and keeps code on grpc.server(). The call ends either way, so I left those alone.

If applicable:

• this PR changes user-facing behavior, and the README is updated
• this PR contains tests

[github-actions]

Perf: server cost per call

Head 9a00c5a against base 1274fc6, 10 rounds in random order on one runner (4 CPUs, grpcio 1.85.1). Run

Scenario	Metric	Base	Head	Change	Head worse	Verdict
low-level unary	CPU µs/call	85.00	84.58	-0.5%	2/10	no change
low-level unary	context switches/call	1.40	1.38	-1.4%	2/10	no change
server() unary	CPU µs/call	142.50	142.50	-0.3%	3/10	no change
server() unary	context switches/call	2.74	2.73	-0.4%	5/10	no change
aio.server() unary	CPU µs/call	120.00	120.00	+0.0%	4/10	no change
aio.server() unary	context switches/call	1.27	1.27	+0.3%	5/10	no change
server() stream	CPU µs/call	300.00	297.92	+0.0%	4/10	no change
server() stream	context switches/call	7.61	7.57	-0.4%	4/10	no change
aio.server() stream	CPU µs/call	283.33	283.33	-0.7%	4/10	no change
aio.server() stream	context switches/call	4.07	4.06	-0.5%	4/10	no change