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
Switches default EVM execution to Giga with parallel OCC for most nodes; only explicit false values keep the old path, which can affect throughput and concurrency behavior on upgrade.

Overview
Giga executor and OCC are now on by default for all nodes that do not explicitly opt out.

DefaultConfig in giga/executor/config/config.go sets Enabled and OCCEnabled to true, so missing giga_executor keys in older TOML configs and newly generated configs both resolve to Giga + OCC unless enabled or occ_enabled is set to false. The embedded config template comments were updated to document the new defaults.

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[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	May 29, 2026, 5:30 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.21%. Comparing base (8567422) to head (dd6aa84).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3521      +/-   ##
==========================================
- Coverage   59.03%   58.21%   -0.82%     
==========================================
  Files        2199     2129      -70     
  Lines      182207   174079    -8128     
==========================================
- Hits       107569   101346    -6223     
+ Misses      64975    63729    -1246     
+ Partials     9663     9004     -659     

Flag	Coverage Δ
sei-chain-pr	60.00% <ø> (?)
sei-db	70.41% <ø> (ø)
sei-db-state-db	?

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

... and 70 files with indirect coverage changes

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