feat: remove CGT dev feature flag

[agusduha]

Note

Removes the CUSTOM_GAS_TOKEN dev feature flag and switches all usage to system/config-based toggles, updating CI, deployer, and tests accordingly.

• Dev features/config:
  • Remove CUSTOM_GAS_TOKEN from DevFeatures.sol, op-deployer (CustomGasTokenDevFlag), and env parsing (Config.devFeatureCustomGasToken).
  • Drop CGT from CI dev-feature matrices in .circleci/config.yml.
  • Feature flag resolver no longer reads DEV_FEATURE__CUSTOM_GAS_TOKEN.
• Deployer:
  • Delete CGT dev flag; integration tests stop setting devFeatureBitmap for CGT and use Intent.CustomGasToken + validate SystemConfig feature.
• Tests (L1/L2/Portal/bridges/fee modules/invariants):
  • Replace skipIfDevFeature* CGT checks with system-level toggles (setUseCustomGasToken(true) or enableCustomGasToken()); remove dev-feature gating throughout.
  • Add/rename CGT-specific test contracts and update test exclusions list.
  • Add CGT-mode variants for OptimismPortal2.depositTransaction/finalizeWithdrawal and L2ToL1MessagePasser tests; convert some checks to view where appropriate.
  • Invariants: switch funding to SafeSend.
• CI:
  • Remove CGT from test matrices; minor workflow cleanups (e.g., add check_changed_patterns where needed).

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