Tightly Pack CB Indices for Reduce + Fused Ops

[edwinleeTT]

Ticket

#16957
#16958

Problem description

CB indices previously had requirements for the values, such as outputs beginning at 16. These requirements were relaxed but the CB indices remained discontinuous, hurting dispatch performance.

What's changed

This PR changes reduction and normalization ops so that circular buffers use the next available index. This will resolve #16957 and resolve #16958.

Checklist

• All post commit CI passes
• Blackhole Post commit CI passes (if applicable)
• Model regression CI passes (if applicable)
• Device performance regression CI passes (if applicable)
• (For models and ops writers) Full new models tests CI passes (if applicable)
• New/Existing tests provide coverage for changes