Feature/global ci fn

[danbraunai-goodfire]

Copied over from #336 with the new dev base branch.

Description

Add global CI function mode as an alternative to the existing layerwise CI functions.

Key changes:

• Add discriminated union config pattern (LayerwiseCiConfig | GlobalCiConfig) for CI function configuration
• Implement GlobalSharedMLPCiFn that concatenates activations across all layers, processes through a shared MLP, and splits outputs back to per-layer CI values
• Add unified wrapper classes (LayerwiseCiFnWrapper, GlobalCiFnWrapper) that provide a consistent interface regardless of CI mode
• Update all experiment configs to new ci_config format
• Add comprehensive tests for both CI modes and checkpoint compatibility validation
• Update canonical runs in registry with new format

Related Issue

N/A

Motivation and Context

The existing layerwise CI functions learn separate importance functions per layer, which limits parameter sharing and may miss cross-layer patterns. Global CI provides an alternative where a single network sees all layer activations simultaneously, enabling:

• Better parameter efficiency for models with many layers
• Potential to learn cross-layer relationships in component importance
• Simpler architecture for experiments where layer-specific CI isn't needed

How Has This Been Tested?

• All tests pass (380 passed locally, CI green)
• New tests added for:
  • Global CI function creation and forward pass
  • Checkpoint compatibility validation between CI modes
  • State dict save/load for both wrapper types
  • Integration with full ComponentModel pipeline
• New canonical runs created with updated config format

Does this PR introduce a breaking change?

Yes. Checkpoints from before this PR are incompatible due to:

• Config format change from flat ci_fn_type/ci_fn_hidden_dims to nested ci_config discriminated union
• State dict key prefix change (now under ci_fn._ci_fns or ci_fn._global_ci_fn)

New canonical runs have been created to replace the old ones.

New Canonical Runs

Experiment	Run ID	WandB Link
tms_5-2	s-38e1a3e2	https://wandb.ai/goodfire/spd/runs/s-38e1a3e2
tms_5-2-id	s-a1c0e9e2	https://wandb.ai/goodfire/spd/runs/s-a1c0e9e2
tms_40-10	s-7387fc20	https://wandb.ai/goodfire/spd/runs/s-7387fc20
tms_40-10-id	s-2a2b5a57	https://wandb.ai/goodfire/spd/runs/s-2a2b5a57
resid_mlp1	s-62fce8c4	https://wandb.ai/goodfire/spd/runs/s-62fce8c4
resid_mlp2	s-a9ad193d	https://wandb.ai/goodfire/spd/runs/s-a9ad193d