op-batcher: improve default throttle parameters

[sebastianst]

Description

Testing showed that the lower threshold is reached too quickly, so it's increased to ~4x 6-blob-transactions. The higher threshold is also increased to widen the throttling range, to 4x the lower threshold, so about ~16x 6-blob-transactions.

The upper tx size throttle limit is also doubled to 20k.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (b4c6919) to head (3c8399c).
⚠️ Report is 22 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #17148       +/-   ##
============================================
- Coverage    45.74%        0   -45.75%     
============================================
  Files         1478        0     -1478     
  Lines       120115        0   -120115     
============================================
- Hits         54945        0    -54945     
+ Misses       61320        0    -61320     
+ Partials      3850        0     -3850     

Flag	Coverage Δ
cannon-go-tests-64	?
contracts-bedrock-tests	?

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see 1478 files with indirect coverage changes

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