fix: record JSON-RPC errors on client OpenTelemetry spans

[mikemikimike]

Summary

Client OpenTelemetry spans did not record JSON-RPC error responses because ErrorData was converted to MCPError after the span context exited. This made failed client requests indistinguishable from successful requests in telemetry.

This change records StatusCode.ERROR, error.type, and rpc.response.status_code while the client span is still active. The existing MCPError behavior is unchanged.

Tests

• uv run --frozen pytest tests/server/test_otel.py -q (17 passed)
• uv run --frozen ruff check src/mcp/shared/jsonrpc_dispatcher.py tests/server/test_otel.py
• uv run --frozen ruff format --check src/mcp/shared/jsonrpc_dispatcher.py tests/server/test_otel.py
• uv run --frozen pyright src/mcp/shared/jsonrpc_dispatcher.py tests/server/test_otel.py
• Full suite with PYTHONUTF8=1: 5574 passed, 16 skipped, 1 xfailed; one unrelated local HTTP 502 failure in tests/client/test_transport_stream_cleanup.py::test_sse_client_closes_all_streams_on_connection_error.

AI assistance was used during development, and the change was reviewed and verified locally.

Fixes #3174

[github-actions]

This PR has been closed automatically. This repo only keeps pull requests open when they come from a maintainer, or from a contributor a maintainer has assigned to the linked issue, and you aren't currently assigned to #3174.

If a maintainer assigns you to #3174, this PR reopens on its own and there's nothing more you need to do here. Assignment is a maintainer call based on capacity; comments that only ask to be assigned don't factor in. What does help is engaging on the issue itself by confirming the repro, explaining why it matters for your use case, or describing the approach you'd take.

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CONTRIBUTING.md has the full reasoning, but in short:

• We're a small team with very little capacity to review community PRs right now.
• Many recent PRs are AI-generated with little human review, and reviewing one carefully still costs a maintainer as much time as it ever did. A well-described issue is usually more useful to us than the code.

Maintainers: reopen, remove missing-issue-link, or add bypass-issue-check to override.