This commit addresses hook alias resolution issues for GPT-OSS MoE models
and adds comprehensive unit tests.

Changes:
1. Fixed JointGateUpMLPBridge hook_aliases to use gate.hook_out instead of
   in.hook_out/input.hook_out, which don't exist in this bridge type
2. Added 7 comprehensive unit tests in test_gpt_oss_moe.py that verify:
   - Model loads without downloading weights (using meta device)
   - Bridge creation works correctly
   - MLP uses JointGateUpMLPBridge (not regular MLPBridge)
   - Compatibility mode hooks are accessible
   - Experts structure is correct (batched tensors, not iterable modules)
   - Hook aliases resolve correctly
   - No incorrect BlockBridge wrapper around experts

Root cause:
- JointGateUpMLPBridge inherits from MLPBridge which has hook_aliases
  expecting in.hook_out or input.hook_out submodules
- JointGateUpMLPBridge creates gate and up submodules instead, causing
  AttributeError when resolving aliases
- Solution: Override hook_aliases at class level to use gate.hook_out

Testing:
All 7 tests pass, verifying GPT-OSS loads correctly and hooks work in
compatibility mode without downloading the full 20B parameter model.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>