Use CachedMemory in bulk-ops executors

[Robbepop]

Locally this yielded a performance improvement for our bulk-ops benchmark test case by roughly 3.5%.
The local test uses memory.copy and memory.fill with 5000 bytes per operation.
Note that performance wins for bulk-ops with smaller lengths are going to be way more significant.

[codecov]

Codecov Report

Attention: Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.47%. Comparing base (c3dc480) to head (cbd684a).

❗ Current head cbd684a differs from pull request most recent head afc3c5f

Please upload reports for the commit afc3c5f to get more accurate results.

Files	Patch %	Lines
crates/wasmi/src/engine/executor/instrs/memory.rs	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1075      +/-   ##
==========================================
- Coverage   80.47%   80.47%   -0.01%     
==========================================
  Files         269      269              
  Lines       24975    24974       -1     
==========================================
- Hits        20099    20097       -2     
- Misses       4876     4877       +1     

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[Robbepop]

Unfortunately, despite the triviality of the changes introduced by this PR local benchmarks indicate extreme performance regressions of 10-20% across the board. Probably the Rust/LLVM optimization heuristics for optimizing the loop+match construct in the interpreter's hot path got confused by this ... again.

[Robbepop]

afc3c5f helped to eliminate all locally observed performance regressions.