feat(giga): use giga executor with OCC by default

[arajasek]

Describe your changes and provide context

This PR makes the giga executor, with OCC enabled, the default behaviour. This means that:

• when a new config TOML is generated, it will have these fields set to true
• when these fields are absent (eg. old config files), the behaviour will default to true

The only nodes not running Giga after this change will be those with these 2 fields explicitly set to false.

Testing performed to validate your change

[cursor]

PR Summary

Medium Risk
Changes the default EVM execution engine for all nodes unless explicitly disabled in config, which affects throughput and execution semantics network-wide; blocktests are isolated via explicit Viper overrides.

Overview
Giga executor and OCC are now on by default for new and legacy configs that omit [giga_executor] flags: DefaultConfig sets enabled and occ_enabled to true, and the config template comments reflect those defaults.

EF blocktest stays on the reference EVM path by forcing giga_executor.enabled and giga_executor.occ_enabled to false in Viper before app.New, so harness checks against EvmKeeper are not affected when node defaults would otherwise enable Giga.

^{Reviewed by Cursor Bugbot for commit 68825a2. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jun 1, 2026, 6:00 PM

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.28%. Comparing base (f8f1af1) to head (68825a2).

Files with missing lines	Patch %	Lines
cmd/seid/cmd/blocktest.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3521      +/-   ##
==========================================
- Coverage   59.12%   58.28%   -0.85%     
==========================================
  Files        2213     2140      -73     
  Lines      182774   174407    -8367     
==========================================
- Hits       108072   101650    -6422     
+ Misses      64985    63719    -1266     
+ Partials     9717     9038     -679     

Flag	Coverage Δ
sei-chain-pr	23.62% <0.00%> (?)
sei-db	70.41% <ø> (ø)
sei-db-state-db	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
giga/executor/config/config.go	60.00% <ø> (ø)
cmd/seid/cmd/blocktest.go	0.00% <0.00%> (ø)

... and 73 files with indirect coverage changes

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