Fix zero-unit stripping inside functions after the first (invalid CSS)

[durvesh1992]

Summary

normalizeZeroDimensions strips redundant units from zero values (0px → 0) but must not do so inside a function — e.g. in calc(0px + 1%), a unitless 0 is a <number> and cannot be added to a <percentage>. It tracks the active function's range via endFunction, but the guard only recorded the first function:

if (node.type === 'function' && !endFunction) {   // only the first function
  endFunction = node.sourceEndIndex ?? 0;
}
if (endFunction > 0 && node.sourceIndex > endFunction) {
  endFunction = 0;                                  // reset once past it
}

postcss-value-parser walks a function node before its children, so when a second function is reached the && !endFunction guard blocks the update, the reset line then zeroes endFunction, and the second function's zero values get their units stripped — producing invalid CSS:

input	output
calc(0px + 1%) (alone)	calc(0px + 1%) ✅
calc(0px + 1%) max(1px,2px) (1st)	calc(0px + 1%) … ✅
max(1px,2px) calc(0px + 1%) (2nd)	max(1px,2px) calc(0 + 1%) ❌

Fix

Record every function's end with Math.max(endFunction, node.sourceEndIndex ?? 0). The existing sourceIndex > endFunction reset still clears the range once walking moves past the last function, so bare zeros outside functions (margin: 0px → 0, calc(5px) 0px → … 0) still normalize correctly.

Test plan

yarn --cwd packages/@stylexjs/babel-plugin jest

Added a regression test (width: 'max(1px, 2px) calc(0px + 1%)' stays calc(0px + 1%)) that fails before and passes after. Full babel-plugin suite: 960 passed, no snapshot regressions.

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