[TOO-1171] feat(arcade-core): add Sentry OAuth2 provider class

[EricGustin]

Add the Sentry OAuth2 provider class

Adds class Sentry(OAuth2) (provider_id = "sentry") so toolkit authors can declare requires_auth=Sentry(), mirroring the existing well-known provider classes, and re-exports it from arcade_tdk.auth and arcade_mcp_server.auth.

Sister to the Engine well-known provider (monorepo, TOO-1170) and the docs page (TOO-1175).

Patch coverage proof

The new class adds a super().__init__ line that only runs on instantiation. libs/tests/core/test_auth_providers.py (added here) parametrizes over every OAuth2 subclass in arcade_core.auth and constructs each, so a newly added provider is covered with no per-provider edit:

Name                                          Stmts   Miss  Cover
libs/arcade-core/arcade_core/auth.py            106      0   100%
============================== 46 passed ==============================

ruff check on the changed files: clean.

Closes TOO-1171

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
libs/arcade-core/arcade_core/auth.py	100.00% <100.00%> (+14.70%)	⬆️
...cade-mcp-server/arcade_mcp_server/auth/__init__.py	100.00% <ø> (ø)
libs/arcade-tdk/arcade_tdk/auth/__init__.py	100.00% <ø> (ø)

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