fix: Remove lingering decimal in return of gweiDecimalToWeiDecimal (#5839)

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This PR aims to fix minor issue on `gweiDecimalToWeiDecimal` utility. 

If given value is more than 9 decimal places then generated WEI value
will have decimal part which we don't expect / want in WEI value.

## References

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Fixes: MetaMask/MetaMask-planning#4973

## Changelog

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## Checklist

- [X] I've updated the test suite for new or updated code as appropriate
- [X] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [X] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs),
highlighting breaking changes as necessary
- [X] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

Author: OGPoyraz

packages/transaction-controller/CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix `userFeeLevel` as `dappSuggested` initially when dApp suggested gas values for legacy transactions ([#5821](https://github.com/MetaMask/core/pull/5821))
 - Fix `addTransaction` function to correctly identify a transaction as a `simpleSend` type when the recipient is a smart account ([#5822](https://github.com/MetaMask/core/pull/5822))
+- Fix gas fee randomisation with many decimal places ([#5839](https://github.com/MetaMask/core/pull/5839))
 
 ## [56.1.0]
 

packages/transaction-controller/src/utils/gas-fees.test.ts

@@ -580,4 +580,37 @@ describe('gweiDecimalToWeiDecimal', () => {
     expect(gweiDecimalToWeiDecimal('1000000')).toBe('1000000000000000');
     expect(gweiDecimalToWeiDecimal(1000000)).toBe('1000000000000000');
   });
+
+  it('handles values with many decimal places', () => {
+    expect(gweiDecimalToWeiDecimal('1.123456789123')).toBe('1123456789');
+    expect(gweiDecimalToWeiDecimal(1.123456789123)).toBe('1123456789');
+  });
+
+  it('handles small decimal values', () => {
+    expect(gweiDecimalToWeiDecimal('0.000000001')).toBe('1');
+    expect(gweiDecimalToWeiDecimal(0.000000001)).toBe('1');
+    expect(gweiDecimalToWeiDecimal('0.00000001')).toBe('10');
+  });
+
+  it('handles string values with leading zeros', () => {
+    expect(gweiDecimalToWeiDecimal('00.1')).toBe('100000000');
+    expect(gweiDecimalToWeiDecimal('01.5')).toBe('1500000000');
+  });
+
+  it('handles string values with trailing zeros', () => {
+    expect(gweiDecimalToWeiDecimal('1.500')).toBe('1500000000');
+    expect(gweiDecimalToWeiDecimal('123.450000')).toBe('123450000000');
+  });
+
+  it('handles extremely small values', () => {
+    expect(gweiDecimalToWeiDecimal('0.000000000001')).toBe('0');
+    expect(gweiDecimalToWeiDecimal(0.000000000001)).toBe('0');
+  });
+
+  it('handles scientific notation inputs', () => {
+    expect(gweiDecimalToWeiDecimal('1e-9')).toBe('1');
+    expect(gweiDecimalToWeiDecimal(1e-9)).toBe('1');
+    expect(gweiDecimalToWeiDecimal('1e9')).toBe('1000000000000000000');
+    expect(gweiDecimalToWeiDecimal(1e9)).toBe('1000000000000000000');
+  });
 });

packages/transaction-controller/src/utils/gas-fees.ts

@@ -126,12 +126,9 @@ export function gweiDecimalToWeiHex(value: string) {
  * // Returns "1500000000"
  */
 export function gweiDecimalToWeiDecimal(gweiDecimal: string | number): string {
-  const gwei =
-    typeof gweiDecimal === 'string' ? gweiDecimal : String(gweiDecimal);
+  const weiValue = Number(gweiDecimal) * 1e9;
 
-  const weiDecimal = Number(gwei) * 1e9;
-
-  return weiDecimal.toString();
+  return weiValue.toString().split('.')[0];
 }
 
 /**