P127: scheduler wakeup/issue eligibility

Forked P126 into P127 and added a shadow scheduler ready-mask model. This records source-use metadata for the integer slot, memory holding record, and control holding record, then samples which held records are source-ready under the P125 architectural busy-bit scoreboard.

Verification:

check	result
`make check-tools`	PASS
P127 Verilator build	PASS
P127 BusyBox shell profile	PASS
`P127-FILE-OK` at cycle	218,572,930
Astro site build	PASS

The important numbers:

scheduler samples       : 43,660,332
any ready               : 37,181,060
none ready              : 6,479,272
single ready            : 37,181,060
dual ready              : 0
triple ready            : 0
integer ready           : 14,855,374
memory ready            : 9,758,720
control ready           : 12,566,966
two-issue opportunities : 0

This is the right negative result to record. The model can see ready work, but the held classes still do not coexist. P128 should model queue/lifetime depth before pretending a multi-issue picker has useful choices.