Add tests and refactor for Simplefin holdings import and processing

- Introduced tests for importer post-import logic and `SimplefinHoldingsApplyJob`.
- Refactored `ProviderImportAdapter` to improve holding resolution strategy.
- Added handling of investment and crypto holdings in importer with debounce logic for job enqueuing.
- Updated rake task to use `SimplefinHoldingsApplyJob` for holding materialization.

lib/tasks/simplefin_holdings_backfill.rake

@@ -124,9 +124,9 @@ namespace :sure do
           if dry_run
             puts({ dry_run: true, sfa_id: sfa.id, account_id: account.id, name: sfa.name, would_process: count }.to_json)
           else
-            SimplefinAccount::Investments::HoldingsProcessor.new(sfa).process
+            SimplefinHoldingsApplyJob.perform_later(sfa.id)
             total_holdings_written += count
-            puts({ ok: true, sfa_id: sfa.id, account_id: account.id, name: sfa.name, processed: count }.to_json)
+            puts({ ok: true, sfa_id: sfa.id, account_id: account.id, name: sfa.name, enqueued: true, estimated_holdings: count }.to_json)
           end
 
           sleep(sleep_ms / 1000.0) if sleep_ms.positive?