test(compliance): add schema-version regression snapshot test

[Ejirowebfi]

Description:

Summary

Adds a snapshot-based regression test for compliance's get_schema_version entrypoint, as requested in #469.

The test hard-codes EXPECTED_SCHEMA_VERSION = 1 and fails immediately if the value changes without a deliberate update to the constant — forcing any
schema bump to be acknowledged, the constant updated, and the storage migration path documented in the PR per #113.

What was checked first

Grepped for get_schema_version and SchemaVersion across all four contracts before writing anything. Result:

• compliance — has get_schema_version and DataKey::SchemaVersion ✓
• invoice — neither exists
• treasury — neither exists
• settlement-workflow — neither exists

The test is correctly scoped to compliance only.

Tests added

contracts/compliance/tests/schema_version_test.rs

Test	What it asserts
schema_version_matches_snapshot	Core regression — get_schema_version() returns exactly EXPECTED_SCHEMA_VERSION = 1
schema_version_available_immediately_after_init	Entrypoint is readable right after initialize, no other calls needed
schema_version_is_stable_across_repeated_reads	Value is deterministic across successive reads

Updating this test in future

If you are intentionally bumping the schema version:

1. Update EXPECTED_SCHEMA_VERSION in this test file to the new value.
2. Add an entry to CHANGELOG.md describing the storage migration path.
3. Include both changes in the same PR.

Closes #469

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