refactor(blob-store): blob store error type

[thomasathorne]

Part of TZX-86.

What

Switch from an associated error type in the BlobStore trait to a dedicated BlobStoreError enum representing the common errors that a blob store may experience (with a Custom variant for other errors associated with specific implementations).

Why

This is an approach that is easier to integrate into other error types such as the existing StorageError in the PVM storage module, which will happen in a follow up PR.

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 75.75758% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.54%. Comparing base (bbf9876) to head (c8ee9b4).

Files with missing lines	Patch %	Lines
data/src/store.rs	42.85%	4 Missing ⚠️
pvm/src/storage.rs	78.57%	2 Missing and 1 partial ⚠️
data/src/store/fold.rs	91.66%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (75.75%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #990      +/-   ##
==========================================
- Coverage   89.59%   89.54%   -0.05%     
==========================================
  Files         125      125              
  Lines       26863    26879      +16     
  Branches    26863    26879      +16     
==========================================
+ Hits        24067    24069       +2     
- Misses       2166     2180      +14     
  Partials      630      630              

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[github-actions]

Benchmark results for revision 3af423f:

Metric	Duration	TPS
Mean	1.519150327s	26.331
Worst	1.52671797s	26.200
Best	1.513712024s	26.425
Standard Deviation	±3.259044ms	±0.056

Full results

Run	Transfers	Duration	TPS
1	40	1.52671797s	26.200
2	40	1.519924723s	26.317
3	40	1.518943436s	26.334
4	40	1.520054628s	26.315
5	40	1.521492468s	26.290
6	40	1.521276961s	26.294
7	40	1.514108127s	26.418
8	40	1.518588821s	26.340
9	40	1.519968967s	26.316
10	40	1.518723269s	26.338
11	40	1.524138168s	26.244
12	40	1.516372379s	26.379
13	40	1.520472637s	26.308
14	40	1.51994412s	26.317
15	40	1.516924216s	26.369
16	40	1.519792797s	26.319
17	40	1.515523283s	26.394
18	40	1.514158874s	26.417
19	40	1.513712024s	26.425
20	40	1.522168669s	26.278

Compare the results above with those for the default branch.