Fix compilation on 32 bit architectures

[jtibshirani]

This PR fixes a bug where Zoekt would not compile on 32-bit architectures. It
also takes the opportunity to start using the math library everywhere instead
of our own constants like maxUInt32 to help prevent this sort of issue in the
future by encouraging devs to select the most accurate "max" type for their
specific situation.

Closes #935

[Copilot]

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (2)

index/matchtree_test.go:309

• [nitpick] Consider revising the error message to use consistent pluralization (e.g. "documents") for clarity.

t.Fatalf("expected %d document, but got at least 1 more", len(want))

index/matchtree.go:676

• [nitpick] The variable name 'minCount' could be made more descriptive to clarify that it stores the minimum number of candidates from the children.

minCount := math.MaxInt