feat(pvm-storage): chunked io using BlobStore

[thomasathorne]

Part of TZX-86.

What

Modify the 'chunked IO' methods commit_serialised and checkout_serialised that are currently used for PVM storage so that they can run against any implementation of the BlobStore trait.

We also add an extension to that trait, ExportStore, that allows copying blobs from one store into another at a given filesystem path. This is needed to implement the export_snapshot method. Having this extra trait will make it easier to switch to using the durable-storage persistence-layer, as that can easily be made to implement ExportStore on top of BlobStore.

Why

We want to benchmark the existing (chunked) commit and checkout as well as the new (folded) methods. If both approaches can be run against an arbitrary BlobStore it makes the benchmarking much easier.

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 56.00000% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.51%. Comparing base (c8ee9b4) to head (c4666a9).

Files with missing lines	Patch %	Lines
pvm/src/storage.rs	52.54%	16 Missing and 12 partials ⚠️
pvm/src/storage/chunked_io.rs	72.72%	0 Missing and 3 partials ⚠️
pvm/src/pvm/node_pvm.rs	60.00%	1 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (56.00%) 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                      @@
##           thomasa/blob-store-error     #993      +/-   ##
============================================================
- Coverage                     89.54%   89.51%   -0.04%     
============================================================
  Files                           125      125              
  Lines                         26879    26896      +17     
  Branches                      26879    26896      +17     
============================================================
+ Hits                          24069    24076       +7     
- Misses                         2180     2189       +9     
- Partials                        630      631       +1     

☔ 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.