Fixes #2578.

Entra ID v2.0 rejects RFC 8707
esource on refresh token requests, and Pydantic AnyHttpUrl normalizes bare-domain URLs with a trailing slash.

Changes:

• Strip the trailing slash when deriving the RFC8707 resource from PRM metadata.
• Do not include
  esource in
  efresh_token grant requests.

Tests:

• uv run --frozen pytest tests/client/test_auth.py -k get_resource_url_strips_trailing_slash_from_bare_domain_prm
• uv run --frozen pytest tests/client/test_auth.py -k refresh_token_request_omits_resource_even_when_required_by_protocol
• uv run --frozen python -m ruff check src/mcp/client/auth/oauth2.py tests/client/test_auth.py
• uv run --frozen python -m ruff format src/mcp/client/auth/oauth2.py tests/client/test_auth.py