Update CI to exercise async test coverage for v1.1

[Mattsface]

Parent: #297

Goal

Update the GitHub Actions test workflow so the v1.1 async transport tests actually run in CI while preserving coverage for the default sync-only installation path.

Why this is needed

The current Offline CI workflow installs dependencies with:

poetry install --no-interaction

Because HTTPX is an optional dependency behind the async extra, the async adapter tests skip in CI when that extra is not installed. The workflow also still targets release/1.0.0 rather than the active release/1.1.0 integration branch.

This creates a coverage gap where the new async transport can appear green locally but receive no meaningful protection from the GitHub Actions matrix.

Scope

Update .github/workflows/build-and-test.yml so that:

• pull requests targeting release/1.1.0 run CI
• pushes to release/1.1.0 run CI
• the existing Python 3.10–3.14 offline-test matrix installs the async extra and therefore executes both synchronous and asynchronous offline tests
• a small separate sync-only job verifies that the default installation still works without HTTPX
• the existing package-build and release-artifact validation flow remains intact unless a change is strictly required for the CI update

Proposed test split

Main offline matrix

Use the existing Python 3.10–3.14 matrix, but install the async extra, for example:

poetry install --no-interaction -E async

This matrix should run the normal offline suite so both sync and async implementation tests execute across all supported Python versions.

Sync-only installation smoke test

Add one lightweight job on a representative supported Python version that installs without extras:

poetry install --no-interaction

Then verify that a normal synchronous import still works without HTTPX, for example:

from mlbstatsapi import Mlb

The purpose of this job is to protect the optional-dependency contract established in #300. It does not need to duplicate the full five-version test matrix.

Out of scope

Do not expand scripts/validate_release.py into full async artifact validation in this issue. Clean-install validation of both python-mlb-statsapi and python-mlb-statsapi[async] belongs with the v1.1 release-validation work in #307.

Do not change async transport behavior in this CI issue.

Do not make HTTPX mandatory for ordinary package installation.

Acceptance criteria

• CI runs for pull requests targeting release/1.1.0
• CI runs for pushes to release/1.1.0
• Python 3.10–3.14 offline matrix installs the async extra
• Async adapter tests no longer skip merely because HTTPX is absent from the CI environment
• Existing synchronous tests continue to run in the same matrix
• A sync-only installation job verifies Mlb remains importable without the async extra
• The optional HTTPX dependency contract from Add optional async dependency and packaging support #300 remains intact
• Package build and existing release-artifact validation continue to pass

Refs #297, #300, #301, #302, #307