Ship the migrators in the TwoMLSPQ product

[germ-mark]

Stacked on #147 and meant to ship in the same release.

The TwoMLSPQMigrate product is removed. Its module now ships in the TwoMLSPQ product. This is breaking: consumers swap .product(name: "TwoMLSPQMigrate") for .product(name: "TwoMLSPQ"). Imports are unchanged.

Why: the internal TwoMLSPQBinding target sat in both products, and Xcode avoids duplicate code per product, not per target. In an Xcode test build, TwoMLSPQ became a shared framework holding one binding copy, while TwoMLSPQMigrate linked statically into the test bundle with a second copy. Each copy keeps its own callback handle map, but Rust keeps a single callback vtable. So a sink installed through one copy is looked up in the other copy's map, and the process aborts with "Callback interface failure" (unexpectedStaleHandle).

Tests

• Checked with a scratch package graph built by xcodebuild: a dynamic framework linking TwoMLSPQ, plus a test bundle linking the TwoMLSPQ products.
  • Before this change, the test binary has its own binding copy and the abort reproduces.
  • After it, only the shared framework holds the binding and the abort is gone.
  • Vending TwoMLSPQBinding as a separate product doesn't help; the abort still reproduces.
• swift test (local xcframework) passes 98 XCTest and 19 Swift Testing tests, and swift-format strict is clean.

🤖 Generated with Claude Code

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Latest commit: 9072ceb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@germ-network/two-mls-pq	Minor

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