Improve the performance of the shielded sync ledger client

[sug0]

Describe your changes

The shielded sync's ledger client continues to perform poorly, even after #3578. This PR introduces some optimizations to the ledger client, and improves its UX a bit.

• Fetches are now logged more frequently on the progress bar. Previously, they weren't being logged because concurrent fetches were starving each other on the first semaphore. To fix this, fetch_shielded_transfers now has a single semaphore point, at the top of the method, rather than two.
• Errors returned from RPC servers are no longer printed. They weren't that helpful anyway, and were spamming the screen, obfuscating the output of the progress bars.
• A linear backoff sleep has been added to the ledger client, on errors, to allow the client to recover from potential rate limiting/throttling imposed by the CometBFT RPC server. On successful fetches, the backoff is reduced, returning to the normal/optimal fetch speed.
• The block batch size parameter has been exposed to the CLI and SDK, allowing users to specify the number of blocks that are fetched per concurrent fetch job. This may help performance, in some cases.

In general, the indexer masp client still performs about 10x better than the ledger masp client, while fetching shielded txs.

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 66.12903% with 21 lines in your changes missing coverage. Please review.

Project coverage is 73.92%. Comparing base (732505c) to head (b2332bf).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/control_flow/time.rs	38.09%	13 Missing ⚠️
crates/sdk/src/masp/utilities.rs	80.48%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4016      +/-   ##
==========================================
- Coverage   73.92%   73.92%   -0.01%     
==========================================
  Files         341      341              
  Lines      106467   106510      +43     
==========================================
+ Hits        78709    78740      +31     
- Misses      27758    27770      +12     

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