v0.0.0-10252-g5c678faf4

[ir] Rewrite `IntervalSet::Normalize` for efficiency.

The normalization process now expands improper intervals and merges overlapping/abutting intervals in-place within the `intervals_` vector, reducing memory allocations and copies. We also take advantage of known information to simplify the overlapping/abutting checks.

PiperOrigin-RevId: 944765711