Hasani 2022 closed-form CfC recurrence; one thread per hidden unit, no
atomicAdd. Tests assert algebraic invariants (dt=0 -> identity, zero
weights -> h_old * decay, large tau -> h_old preserved, output bound).
Also removes src/cfc/oracle.rs and replaces snap_feature bit-equiv
test with property assertions per feedback_no_cpu_test_fallbacks.md.
CPU mirrors are bug-locks; validation is now via known synthetic
inputs + analytical relations on the GPU output.
12 tests pass on local sm_86 (7 snap_feature invariants + 5 cfc_step
invariants).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
f927469ed3