✨ Add missing BQSKit synthesis passes

[flowerthrower]

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Description

Adds the two BQSKit synthesis actions used by the paper prototype but missing from the production action registry:

• QSDPass
• MGDPass

Both actions reuse the existing partitioned-synthesis factory, including its established model, seed, partitioning, retargeting, and measurement handling. FullQSDPass remains a separate action.

This draft is stacked on #759. It intentionally contains only the raw action additions; documentation and new tests are deferred.

Validation

• imported the action registry with BQSKit 1.2.1
• verified the action order around WalshDiagonalSynthesisPass and FullQSDPass
• git diff --check

Checklist

• The pull request only contains focused changes required for this feature.
• New tests and documentation are intentionally deferred while the feature stack is assembled.
• I reviewed the complete base-to-head diff.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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