Build warnings in template for intervaltree.pxi

The scalar_t fused type

pandas/pandas/_libs/intervaltree.pxi.in

Lines 9 to 14 in b115a6b

	ctypedef fused scalar_t:
	float64_t
	float32_t
	int64_t
	int32_t
	uint64_t

mixes signed and unsigned types. Later on, the code does comparisons with unsigned types, which creates a bunch of compiler warning.

xref http://docs.cython.org/en/latest/src/userguide/fusedtypes.html#type-checking-specializations

From comments in #27157 it appears there's no established guideline on how different cases for different types should look like in the templates. That's a hindrance to fixing this (and other warnings) as well.