Addresses failures with the following, in some files:
-Wshorten-64-to-32
-Wimplicit-int-conversion
-Wsign-compare
-Wsign-conversion
-Wtautological-unsigned-zero-compare

(This specific CL focuses on .cc files in */internal/.)

Bug: chromium:1292951
PiperOrigin-RevId: 471561809
Change-Id: I7abd6d83706f5ca135f1ce3458192a498a6280b9