PoS: fix and improve chained redelegation error msg

[tzemanovic]

Describe your changes

closes #4263

The args for IncomingRedelIsStillSlashable error were swapped. Also added the earliest redelegation epoch to help users determine when they can redelegate again.

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 0% with 16 lines in your changes missing coverage. Please review.

Project coverage is 74.04%. Comparing base (e36982c) to head (8eca9f8).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/sdk/src/tx.rs	0.00%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4264      +/-   ##
==========================================
- Coverage   74.06%   74.04%   -0.03%     
==========================================
  Files         345      345              
  Lines      109871   109877       +6     
==========================================
- Hits        81372    81354      -18     
- Misses      28499    28523      +24     

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[brentstone]

Thx a bunch LGTM