feat!: Add a default transaction limit

[evan-forbes]

Overview

this PR is the quick solution to #1209. Note that this is not a new block validity rule, only an extra check during PrepareProposal.

Checklist

• New and updated code has appropriate documentation
• New and updated code has new and/or updated testing
• Required CI checks are passing
• Visual proof for any user facing features like CLI or documentation updates
• Linked issues closed with keywords

[codecov-commenter]

Codecov Report

Merging #1210 (6be211e) into main (f4f6a3a) will decrease coverage by 0.08%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1210      +/-   ##
==========================================
- Coverage   48.08%   48.00%   -0.09%     
==========================================
  Files          72       72              
  Lines        4082     4089       +7     
==========================================
  Hits         1963     1963              
- Misses       1947     1954       +7     
  Partials      172      172              

Impacted Files	Coverage Δ
app/prepare_proposal.go	0.00% <0.00%> (ø)
app/process_proposal.go	0.00% <0.00%> (ø)
x/blob/types/blob_tx.go	18.57% <0.00%> (+1.90%)	⬆️

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