fix(sdk-coin-flrp): use assert for bigint comparisons in import fee tests

should.above() coerces to number and fails on bigint values, breaking the
build. Compare with native > via assert instead.

Ticket: CECHO-1821

Author: ArunBala-Bitgo

modules/sdk-coin-flrp/test/unit/lib/importInCTxBuilder.ts

@@ -252,7 +252,10 @@ describe('Flrp Import In C Tx Builder', () => {
 
       // The gas-aware fee (including the real AtomicTxBaseCost, ~10,000) must exceed
       // the underpriced legacy estimate that caused "insufficient funds" on broadcast.
-      actualFee.should.be.above(underpricedFee);
+      assert(
+        actualFee > underpricedFee,
+        `Expected actualFee (${actualFee}) to be above underpricedFee (${underpricedFee})`
+      );
     });
 
     it('should pad the supplied base fee to absorb volatility between signing and broadcast', async () => {
@@ -276,7 +279,9 @@ describe('Flrp Import In C Tx Builder', () => {
       // Same input should be deterministic, and strictly greater than the raw baseFee * gas
       // (i.e. some padding is applied on top of the network-observed base fee).
       BigInt(paddedTx.fee.fee).should.equal(BigInt(unpaddedFeeEquivalentTx.fee.fee));
-      BigInt(paddedTx.fee.fee).should.be.above(baseFeeWei * 11300n); // > known real gas cost * baseFee, proving padding
+      const paddedFee = BigInt(paddedTx.fee.fee);
+      const minExpectedFee = baseFeeWei * 11300n; // > known real gas cost * baseFee, proving padding
+      assert(paddedFee > minExpectedFee, `Expected paddedFee (${paddedFee}) to be above ${minExpectedFee}`);
     });
   });