feat: migrate from flight-grpc to flight-core

[bednar]

Proposed Changes

The flight-grpc package is no longer maintained and was considered experimental, providing utility classes to expose both a Flight gRPC service and a client.

In our case, we don’t need to expose a gRPC service—the client alone is sufficient for our needs.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• Tests pass
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.59%. Comparing base (2d41c39) to head (7188b13).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #202   +/-   ##
=======================================
  Coverage   89.59%   89.59%           
=======================================
  Files          17       17           
  Lines         903      903           
  Branches      137      137           
=======================================
  Hits          809      809           
  Misses         38       38           
  Partials       56       56           

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[karel-rehor]

Tests pass locally. Updates make sense.