fix(gov): parse expedited proposal responses

[ChrisWozniak]

Proposed Changes

• Allow Governance proposal REST responses to contain fields newer than the generated Proposal protobuf model.
• Add regression tests for single-proposal and proposal-list responses containing is_expedited.

Linked Issues

Fixes #364

Types of changes

• Bug fix (non-breaking change that fixes an issue).
• New feature added (non-breaking change that adds functionality).
• Breaking change (fix or feature that would cause existing functionality to stop working as expected).
• Documentation update.
• Something else (e.g., tests, scripts, example, deployment, infrastructure).

Checklist

• I have read the CONTRIBUTING guide.
• Checks and tests pass locally.

If applicable

• I have added tests that prove my fix is effective or that my feature works.
• I have checked that code coverage does not decrease.
• I have added/updated the documentation.

Further comments

The generated cosmos.gov.v1beta1 Proposal model predates is_expedited. Ignoring unknown response fields restores compatibility without a broad protobuf regeneration; all currently modelled proposal fields continue to parse.