Make MerkleLayer modal

[kurtisc]

Closes RV-902

What

Refactors MerkleLayer to pass off methods to a modal implementation.

Why

We will need to be able to implement these for Proof and Verify modes.

How

• Adds a new trait MerkleLayerMode
• Implements the trait for Normal
• Makes MerkleLayer generic over this trait
• Implements the functionality using this trait for Normal

Manually Testing

make all

Tasks for the Author

• Link all Linear issues related to this MR using magic words (e.g. part of, relates to, closes).
• Eliminate dead code and other spurious artefacts introduced in your changes.
• Document new public functions, methods and types.
• Make sure the documentation for updated functions, methods, and types is correct.
• Add tests for bugs that have been fixed.
• Explain changes to regression test captures when applicable.
• Write commit messages in agreement with our guidelines.
• Self-review your changes to ensure they are high-quality.
• Complete all of the above before assigning this MR to reviewers.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.05%. Comparing base (5b58082) to head (f0fdcbd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #792      +/-   ##
==========================================
- Coverage   91.08%   91.05%   -0.03%     
==========================================
  Files         110      110              
  Lines       20831    20831              
  Branches    20831    20831              
==========================================
- Hits        18973    18968       -5     
- Misses       1485     1490       +5     
  Partials      373      373              

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[github-actions]

Benchmark results for revision abbcbf7:

Metric	Duration	TPS
Mean	1.51829718s	26.346
Worst	1.524812298s	26.233
Best	1.504052573s	26.595
Standard Deviation	±4.881075ms	±0.085

Full results

Run	Transfers	Duration	TPS
1	40	1.521765301s	26.285
2	40	1.522225705s	26.277
3	40	1.52171415s	26.286
4	40	1.518219838s	26.347
5	40	1.513157899s	26.435
6	40	1.523211357s	26.260
7	40	1.520445329s	26.308
8	40	1.514268249s	26.415
9	40	1.524181318s	26.244
10	40	1.522987981s	26.264
11	40	1.520644593s	26.305
12	40	1.519884936s	26.318
13	40	1.524812298s	26.233
14	40	1.504052573s	26.595
15	40	1.513375014s	26.431
16	40	1.513877496s	26.422
17	40	1.515424185s	26.395
18	40	1.516748695s	26.372
19	40	1.517188278s	26.365
20	40	1.517758415s	26.355

Compare the results above with those for the default branch.