feat(Merkle): partially implement Verify mode

[kurtisc]

Part of RV-959

What

Implements (most of) Verify mode for the Merkle layer

Why

We want to move towards Verify and Prove mode implementations up to the Registry. This is a prerequisite.

How

• Introduces VerifyImpl and MerkleLayer<KV, Verify>::from_verify_tree
• Fills in 'impl MerkleLayerMode for Verify', delegating to MerkleLayerMode
• Moves the VerifyTreeId::Default impl and makes default trees present. This makes sense to me as nodes that are created or rebalanced must be present, but is worth revisiting during implementation of the round-trip tests.

Doesn't implement proof parsing yet, which needs RV-958 and will allow construction of a Verify Merkle layer in production.

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

❌ Patch coverage is 95.20000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.60%. Comparing base (bbf9876) to head (08db65e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
durable-storage/src/merkle_layer.rs	94.95%	2 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #991      +/-   ##
==========================================
+ Coverage   89.59%   89.60%   +0.01%     
==========================================
  Files         125      125              
  Lines       26863    26985     +122     
  Branches    26863    26985     +122     
==========================================
+ Hits        24067    24181     +114     
- Misses       2166     2171       +5     
- Partials      630      633       +3     

☔ View full report in Codecov by Sentry.
📢 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.

[github-actions]

Benchmark results for revision b4a0ebe:

Metric	Duration	TPS
Mean	1.521731716s	26.286
Worst	1.531862093s	26.112
Best	1.515722048s	26.390
Standard Deviation	±4.119041ms	±0.071

Full results

Run	Transfers	Duration	TPS
1	40	1.522020167s	26.281
2	40	1.52993071s	26.145
3	40	1.515952745s	26.386
4	40	1.527047935s	26.194
5	40	1.52248531s	26.273
6	40	1.519050031s	26.332
7	40	1.515722048s	26.390
8	40	1.520506621s	26.307
9	40	1.52177013s	26.285
10	40	1.519245307s	26.329
11	40	1.531862093s	26.112
12	40	1.519437723s	26.326
13	40	1.523201539s	26.260
14	40	1.518486865s	26.342
15	40	1.518636675s	26.339
16	40	1.519426261s	26.326
17	40	1.525768059s	26.216
18	40	1.523330257s	26.258
19	40	1.521015482s	26.298
20	40	1.519738361s	26.320

Compare the results above with those for the default branch.