feat(insurance): add cursor pagination tests for active policy listing

[Arowolokehinde]

Add comprehensive unit tests in insurance/src/test.rs covering get_active_policies pagination semantics:

• Empty results, single policy, cursor progression across pages
• Inactive policy exclusion (partial and full deactivation)
• Stable ID-ascending ordering guarantee
• Cursor skip over inactive gaps
• Cursor past last ID returns empty
• next_cursor equals last returned ID on full pages, zero on final page
• count field always matches items.len()
• No duplicates across paginated responses
• Limit clamping: zero -> DEFAULT_PAGE_LIMIT, above max -> MAX_PAGE_LIMIT
• Per-owner isolation between different users
• Core contract functions: create, get, deactivate, pay_premium, batch_pay_premiums, get_total_monthly_premium, set_pause_admin

Also fixes pre-existing build errors:

• stress_tests.rs: correct create_policy call signature (CoverageType enum instead of String, add missing external_ref argument)
• remittance_split/Cargo.toml: remove duplicate proptest key

Closes #519