namada Refactor shielded sync

Describe your changes

This PR refactors shielded sync to make the following improvements

Allow fetching new masp txs and trial-decrypting notes to happen asynchronously
Parallelize the trial-decryptions
Modularize the logic so that we can mock parts of the algorithm for tests and to enable migration over to using a specila masp indexer
Added test coverage
Decouple nullifying notes and updating spent notes from the trial-decryption process
Refactor the masp.rs module in the sdk into several smaller files and submodules

The new architecture of the algorithm can be found here

N.B. The integration tests seem flaky on the CI, although I can't reproduce any of it locally. It's unclear to me if it is due to the changes in this PR.

Indicate on which release or other PRs this topic is based on

Checklist before merging to `draft`

[x] I have added a changelog
[x] Git history is in acceptable state

Apr 04 '24 15:04 batconjurer

Codecov Report

Attention: Patch coverage is 46.65658% with 1763 lines in your changes missing coverage. Please review.

Project coverage is 54.73%. Comparing base (883bd0f) to head (bdb61c3).

Files	Patch %	Lines
crates/sdk/src/masp/shielded_ctx.rs	51.29%	844 Missing :warning:
crates/sdk/src/masp/mod.rs	29.79%	436 Missing :warning:
crates/sdk/src/masp/utils.rs	51.28%	208 Missing :warning:
crates/apps_lib/src/client/masp.rs	0.00%	186 Missing :warning:
crates/sdk/src/masp/types.rs	72.61%	43 Missing :warning:
crates/node/src/bench_utils.rs	0.00%	27 Missing :warning:
crates/sdk/src/masp/test_utils.rs	89.79%	15 Missing :warning:
crates/apps_lib/src/cli/client.rs	0.00%	2 Missing :warning:
crates/node/src/lib.rs	0.00%	1 Missing :warning:
crates/sdk/src/tx.rs	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3006      +/-   ##
==========================================
+ Coverage   54.05%   54.73%   +0.67%     
==========================================
  Files         315      319       +4     
  Lines      106296   107702    +1406     
==========================================
+ Hits        57461    58952    +1491     
+ Misses      48835    48750      -85

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