allow wrap-around of PL_cop_seqmax

allow wrap-around of PL_cop_seqmax

After a large number of evals, PL_cop_seqmax (a U32) will wrap around
again to zero. Make the code handle this case by:

1) When incrementing PL_cop_seqmax, never allow its value to become
   equal to PERL_PADSEQ_INTRO;
2) When testing for COP_SEQ_RANGE_LOW < seq <= COP_SEQ_RANGE_HIGH,
   allow for the fact that _HIGH may be lower than _LOW.

This is a final fix for  [perl #83364].