Migrate tasks from Makefile to poe

[anuraaga]

Fixes #474

We like to use poe now for Python projects. For reference, connect-python

This also

• Vendors in protovalidate protos as suggested in https://github.com/bufbuild/protovalidate-python/pull/473/changes/BASE..d961b4859dfdca06b125d549bb3635d778ab892a so we can make local edits when needed while otherwise being synced with upstream
• Replaces pytest pythonpath setup with fix-protobuf-imports making protos relative
• Takes advantage of python scripts to simplify certain generation commands

[jonbodner-buf]

is this a stale reference to Makefile?

[jonbodner-buf]

Issues found by Claude:

• uv sync --frozen silently breaks the lowest-direct matrix leg

  The ci job runs a matrix over resolution: ["highest", "lowest-direct"] via UV_RESOLUTION. The old make install ran plain uv sync, which honors UV_RESOLUTION and actually resolves the lowest direct deps. The migration changed this to uv sync --frozen and --frozen installs exactly what's in uv.lock, ignoring UV_RESOLUTION entirely. So the lowest-direct leg now installs the same locked (highest) versions as highest; it tests nothing. This also explains why the dropped CI comment mattered:

# When running with matrix.resolution == lowest-direct, we expect uv.lock to change, but we don't want that file checked in.

That comment was attached to make checkgenerate and is gone. The fix is to not use --frozen in the ci job (keep it only where you want frozen, e.g. lint).

• Code generation is no longer a clean regen

  The old make generate did rm -rf src && mkdir ... and rm -rf gen before regenerating. The new scripts/generate_protovalidate.py / generate_cel.py / generate-test do no cleanup (confirmed — no rmtree/rm). buf export/buf generate overwrite and add files but never delete, so a proto removed upstream leaves an orphaned *_pb2.py/.pyi that poe diffcheck won't catch (the orphan is already committed → no diff). The migration lost the clean-slate guarantee.

[jonbodner-buf]

couple more Claude-discovered issues:

• poe format doesn't format protos, but poe lint checks them

  Old make format ran buf format --write. The new format task is only format-python + format-toml + add-license-header — no proto formatting. Meanwhile lint-protos still runs buf format -d --exit-code. A contributor with a misformatted .proto (there are hand-written ones: proto/tests/example/v1/validations.proto, test/proto/...) can't fix it with poe format and will fail poe lint. Add a format-protos (buf format -w) step.

• PROTOVALIDATE_VERSION is no longer overridable

  poe_tasks.toml sets it as a hard [env] value:

  [env]
  PROTOVALIDATE_VERSION = "v1.2.0"

The Makefile used ?= (overridable from the shell). poe's plain [env] assignment overrides the host env, so PROTOVALIDATE_VERSION=… uv run poe generate no longer works. Use the default form:

PROTOVALIDATE_VERSION.default = "v1.2.0".

[anuraaga]

Thanks fixed them