workflow extra's anyio<4.7 pin blocks the mcp extra (anyio>=4.9)

[LukasGold]

osw[workflow] and osw[mcp] cannot be installed into the same environment.

• osw[workflow] pins anyio>=4.4.0,<4.7
• mcp>=2 requires anyio>=4.9 (anyio>=4.10 on Python 3.14+)

No anyio version satisfies both, so uv lock fails when both extras are resolvable together.

Why the anyio cap exists

prefect 2.20.25's GatherTaskGroup subclasses anyio's TaskGroup but does not
implement create_task, which newer anyio made abstract. Broken on anyio 4.14,
verified good on 4.6.2. prefect 2.20.25 is the final 2.x release, so no backport
is coming.

Current workaround

Applied in #133:

1. [tool.uv] conflicts declares the mcp extra mutually exclusive with both the
   workflow extra and the dev dependency-group.
2. mcp is excluded from the all extra and from the dev group, so the default
   resolution keeps the workflow-compatible anyio.
3. The dev group lists prefect and anyio directly instead of inheriting them
   from osw[workflow]. Being in a conflict set, a self-referential osw[workflow]
   entry would only activate under --extra workflow, leaving a bare uv sync on
   anyio 4.14 (the version that breaks prefect). These pins now have to be kept in
   sync with the workflow extra by hand.
4. The pytest stack moved into its own test group, since dev conflicts with the
   mcp extra and there would otherwise be no environment containing both pytest
   and mcp.
5. src/osw/mcp is excluded from ty, since its imports are unresolvable in the
   default dev environment.
6. The MCP unit tests use importorskip, so they skip in the default suite.

Cost

The MCP server module is neither type-checked nor unit-tested in the default
environment. Its tests pass (32 passed against mcp==2.0.0) but only when run
explicitly:

uv sync --extra mcp --group test --no-dev
uv run --extra mcp --group test --no-dev --no-sync python -m pytest tests/test_mcp_*.py

CI does not currently run that second environment.

What to check

Whether the anyio cap is still needed, either because a newer anyio restored the
non-abstract create_task path, or because the workflow extra can move to
prefect 3.x. If the cap can be lifted, revert all six workarounds above and put
mcp back into all and dev.