End epochs for continuous PGF distributions

[brentstone]

Describe your changes

Closes #4104

Todo:

• update the Remove variant for cont PGF to remove by address + proposal ID

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 62.96296% with 70 lines in your changes missing coverage. Please review.

Project coverage is 74.51%. Comparing base (4558855) to head (8177ad2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/governance/src/pgf/inflation.rs	31.25%	33 Missing ⚠️
crates/governance/src/finalize_block.rs	16.66%	20 Missing ⚠️
crates/governance/src/storage/proposal.rs	73.80%	11 Missing ⚠️
crates/sdk/src/signing.rs	94.11%	4 Missing ⚠️
crates/sdk/src/rpc.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4408      +/-   ##
==========================================
- Coverage   74.54%   74.51%   -0.03%     
==========================================
  Files         339      339              
  Lines      110504   110592      +88     
==========================================
+ Hits        82372    82407      +35     
- Misses      28132    28185      +53     

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