fix: support decimal multivariate variation weights

[SahilJat]

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Changes

Closes #7671

This PR enables support for decimal/fractional values in multivariate variation weights within the dashboard.

Key updates:

• Updated VariationValueInput.tsx to use a number input type with step="any", allowing for decimal entry.
• Replaced parseInt with parseFloat in the variation weight change handler to ensure decimal values are preserved in the state.
• Updated the calculateControl utility in utils.tsx to round the calculated control remainder to 2 decimal places, preventing floating-point precision artifacts (e.g., 0.09999999999999432) from appearing in the UI.

How did you test this code?

• Manual Verification: Verified that decimal weights (e.g., 0.1 and 99.9) can now be entered and saved through the dashboard without being rounded to integers.
• UI Logic Verification: Confirmed that the "Control Value" percentage correctly calculates and displays as a clean decimal (e.g., 0.1%) when other variations total 99.9%.
• Regression Testing: Reviewed existing E2E test patterns to ensure that switching from type="text" to type="number" does not break existing automation that interacts with these fields.

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