Fixes MASP tx expiration in the SDK

[grarco]

Describe your changes

Closes #3586.

• Fixes a bug by which the SDK would not set the correct expiration to MASP Transactions
• Adds an integration test for masp expiration
• Removes some outdated assertions based on the old double-block execution scheme
• Improves assertions on MockNode
• Wraps MockNode into a single Arc

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

[codecov]

Codecov Report

Attention: Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.

Project coverage is 72.49%. Comparing base (ef49b3d) to head (f41e88a).
Report is 34 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/sdk/src/tx.rs	66.66%	2 Missing ⚠️
crates/shielded_token/src/masp/shielded_wallet.rs	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3724      +/-   ##
==========================================
- Coverage   72.50%   72.49%   -0.01%     
==========================================
  Files         338      338              
  Lines      104190   104191       +1     
==========================================
- Hits        75541    75538       -3     
- Misses      28649    28653       +4     

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[sug0]

couple of suggestions + comments