Add upgrade migration state compatibility tests

[dekaptain2]

PR: Upgrade/Migration Test Harness

Summary

This PR adds regression coverage for Aid Escrow contract upgrade and migration behavior.

What changed

• Added migration progression tests covering a real version path from v1 to v2 to v3.
• Added state compatibility assertions to ensure migrations preserve core contract state:
  • contract version
  • admin identity
  • config values
  • pause state
• Added invalid-transition coverage so repeated or downgraded versions fail with a clear InvalidState error.

Why

These tests make upgrade and migration rules explicit and help prevent regressions where state compatibility breaks across contract versions.

Testing

• Added/updated Rust contract tests in the Aid Escrow versioning suite.
• Verification was attempted locally, but the current Windows Rust toolchain environment blocked cargo execution with a local toolchain error.

Notes

• Branch: feature/573-upgrade-migration-test-harness
• Commit: c3ca6c5

Closes #573

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[Cedarich]

@dekaptain2 fix workflow