P119 - LSU request scoreboard

P119 adds a shadow LSU request record plus scoreboard-style busy accounting. It is not a real decoupled LSU yet; memory operations still retire in order through the existing execute and S_MEM states.

The shell profile is PASS:

post-load cycles    : 218,814,345
shell window cycles : 64,930,511
retired instructions: 86,364,977
CPI                 : 2.5336
S_FETCH cycles      : 7,630,872
S_MEM cycles        : 27,749,744

Request-record counters:

allocs           : 27,889,983
completes        : 27,749,744
flushes          : 443
busy cycles      : 30,685,198
scoreboard busy  : 30,685,198
valid at end     : 0

Honest status: RTL simulation PASS. LibreLane hardening is NOT RUN.