Pin RemitwiseEvents topic taxonomy tests

[Dreamstore2046]

Closes #1035.\n\n## Summary\n- add tests pinning every EventCategory discriminant\n- add tests pinning every EventPriority discriminant\n- assert RemitwiseEvents::emit publishes the (Remitwise, category, priority, action) topic tuple and payload\n- assert RemitwiseEvents::emit_batch publishes the fixed batch topic tuple and (action, count) payload, including zero-count batches\n- document the regression coverage in docs/EVENT_TAXONOMY.md\n\n## Validation\n- git diff --check\n\n## Notes\n- I could not run cargo fmt/test locally because this Windows environment does not have cargo/rustfmt installed (cargo and
ustfmt are not recognized on PATH). The patch is limited to remitwise-common tests plus taxonomy docs so CI should exercise the Rust validation.

[Dreamstore2046]

CI follow-up:

• I removed unwrap/expect usage from the new emit taxonomy tests and force-pushed the branch.
• The rerun now has Security Checks, Gas Benchmarks, and Storage Key Naming passing.
• Build/Test, Validate/Build, and the unwrap/expect lint job are still blocked before reaching this test change by existing reporting/src/lib.rs compile errors, e.g. missing ToI128Checked in scope and ? used in a function returning u32.
• Local validation available in this environment: git diff --check passes. This Windows environment does not have cargo/rustfmt installed, so I am relying on GitHub Actions for Rust validation.

[Dreamstore2046]

Follow-up push:

I also added a minimal reporting compile unblock because the full workspace CI was failing before it could validate this PR's remitwise-common tests. The reporting changes are limited to:

• returning the computed bill compliance percentage from the existing else branch;
• wrapping the coverage-to-premium ratio calculation in a block that returns the converted value;
• replacing a Result-returning conversion inside calculate_savings_score with a bounded fallback because that helper returns u32.

I kept the changes unwrap/expect-free and verified git diff --check locally.

[Dreamstore2046]

Latest CI status after the follow-up pushes:

• Soroban Smart Contracts CI is now green: Build and Test, Lint, Security Checks, Storage Key Naming, and Gas Benchmarks all pass on 57792de.
• The earlier reporting compile blockers were fixed, and the emit taxonomy tests are formatted and unwrap/expect-free.
• Batch-B CI Gate still fails, but it is now past the earlier reporting/bill pagination blockers and fails in family_wallet all-features tests with repeated HostError: Error(Auth, ExistingValue) during FamilyWalletClient::init across many unrelated tests.

I stopped short of broadening this PR into a family_wallet test/auth refactor because that failure appears outside the event taxonomy change and would be much larger than this issue's scope.

[Baskarayelu]

thanks for the contribution! please get assigned to the issue before raising a PR (no assigned issue is linked to you here). closing as invalid for now 🙏