Murisi/sequential payment addresses

[murisi]

Describe your changes

Implemented deterministic shielded payment address generation replacing the former method of randomly generating payment addresses. Determinism is achieved by maintaining a diversifier index for each viewing key in the wallet store and incrementing it each time a payment address is generated. Specifically, the following changes have been made:

• Extended the wallet store with a diversifier index field
• Implemented migration so the wallet can read older Store versions that do not contain diversifier indices
• Extended the gen-payment-addr CLI command with a flag to set the current diversifier index for a viewing key
• Altered payment address generation to use stored/specified diversifier index and increment it afterwards

A drawback of the approach taken is that gen-payment-addr must now take the alias of a viewing key as its argument instead of a literal viewing key. This is because it needs to have an alias to write the updated diversifier index back to. But under the assumption that end-users were not calling gen-payment-addr with literal keys, the CLI command can continue to be used in exactly the same way as before.

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

Attention: Patch coverage is 25.86207% with 86 lines in your changes missing coverage. Please review.

Project coverage is 74.48%. Comparing base (b5f4a7d) to head (a64db62).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/masp.rs	0.00%	47 Missing ⚠️
crates/wallet/src/store.rs	55.55%	24 Missing ⚠️
crates/wallet/src/lib.rs	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4417      +/-   ##
==========================================
- Coverage   74.52%   74.48%   -0.04%     
==========================================
  Files         339      339              
  Lines      110504   110615     +111     
==========================================
+ Hits        82351    82395      +44     
- Misses      28153    28220      +67     

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