KeyGen's Keccak consumers (G/H via sha3, A via SampleNTT, C via CBD) run in
disjoint top-FSM phases, so one keccak_core suffices. Add sha3_top_shared
(keccak_core externalised as kc_* ports, like the existing sample_*_shared
variants); mlkem_top now instantiates one keccak_core and a phase mux that
routes kc_state_i/kc_valid_i from the active consumer and gates kc_valid_o
per consumer (inactive samplers latch squeeze state unconditionally).
Cuts the KeyGen datapath from 4 keccak_core (1600-bit state + 24-round logic
each) to 1 -- the dominant ASIC area win. 11/11 KAT PASS (K=2 c0-4, K=3/4
c0-2), byte-exact, 0 file-not-found.
FallenSigh
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