fix(predict): round fee decimals to avoid underflow errors (#22361)

## **Description**

Fixed a floating-point precision issue in the Polymarket fee calculation
that was causing order placement failures. When calculating fees (e.g.,
for a $7.40 bet), JavaScript floating-point arithmetic would produce
values with excessive decimal places (e.g., 0.29600000000000004), which
would later fail when passed to `parseUnits`. The fix rounds the fee to
4 decimal places to prevent these precision errors while maintaining
sufficient accuracy for fee calculations.

## **Changelog**

CHANGELOG entry: null

## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: Polymarket bet placement

  Scenario: user places a bet with amount that triggers floating-point precision issue
    Given user is on the Predict feature
    And user has selected a Polymarket prediction market

    When user enters a bet amount of $7.40
    And user confirms the bet placement
    Then the order should be successfully placed without errors
```

## **Screenshots/Recordings**

### **Before**

Order placement would fail with parseUnits error when fee calculation
resulted in values like 0.29600000000000004

### **After**

Order placement succeeds as fee is properly rounded to 0.2960 (4 decimal
places)

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Round `totalFee` to 4 decimals in `calculateFees` to prevent
floating-point precision issues.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
b198cda. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: matallui

app/components/UI/Predict/providers/polymarket/utils.ts

@@ -756,6 +756,9 @@ export async function calculateFees({
 
   totalFee = (userBetAmount * FEE_PERCENTAGE) / 100;
 
+  // Round to 4 decimals
+  totalFee = Math.round(totalFee * 10000) / 10000;
+
   // split total 50/50 between metamask and provider
   const metamaskFee = totalFee / 2;
   const providerFee = totalFee - metamaskFee;