Allow hoisting invariant factors in rfactor

[alexreinking]

This PR adds a mode to rfactor that hoists invariant factors according to a detected distributive (semiring) law into the write-back part of the accumulation step. This enables writing straightforward quantized kernels in the algorithm language and factoring them into efficient kernels.

On my system (Apple M3 Max, 1 core), the schedule in test/performance/tiled_matmul_arm_neon.cpp outcompetes existing schedules:

Quantized mat-vec (int8 x int8 -> f32, SDOT)
Time with non-hoisting rfactor:  0.0871 ms
Time with hoisted rfactor:       0.0122 ms (7.13x vs non-hoisting)

The difference in performance is in mostly due to hoisted rfactor's ability to target SDOT instructions.

Breaking changes

No breaking changes. The mode is 100% opt-in.

Just like rfactor, it is possible to write equivalent algorithms that can be scheduled equally well. However, doing so is relatively finicky and more complicated.

Checklist

• Tests added or updated (not required for docs, CI config, or typo fixes)
• Documentation updated (if public API changed)
• Python bindings updated (if public API changed)
• Benchmarks are included here if the change is intended to affect performance.
• Commits include AI attribution where applicable (see Code of Conduct)

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 68 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@2fad88f). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/IROperator.cpp	36.66%	16 Missing and 22 partials ⚠️
src/Func.cpp	84.03%	6 Missing and 13 partials ⚠️
src/Func.h	33.33%	6 Missing ⚠️
src/AssociativeOpsTable.cpp	66.66%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9190   +/-   ##
=======================================
  Coverage        ?   69.37%           
=======================================
  Files           ?      254           
  Lines           ?    78427           
  Branches        ?    18789           
=======================================
  Hits            ?    54409           
  Misses          ?    18503           
  Partials        ?     5515           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.