cache knobs: env-parameterize geth/op-geth --cache (default 1024 = geth's own), l2geth --cache (default 8192 = previous hardcoded), nethermind MEMORYHINT (default 2048000000)

All defaults preserve current effective behavior - this deploy is a rendering no-op
until a host_var overrides a value. Part of the resource-optimizer knob rollout
(resource-optimizer/knob-manifest.yaml is the registry; verify_manifest.py enforces
default sync between templates and envfile).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

op/geth/hashkeychain-testnet-op-geth-pruned-pebble-path.yml

@@ -75,6 +75,7 @@ services:
     entrypoint: /bin/sh -c '[ -f /config/genesis.json ] && geth --db.engine=pebble --gcmode=full --datadir /data init --state.scheme=path /config/genesis.json; exec geth "$@"' --
     command:
       - --bootnodes=enode://0492e74fb10579a3c53a327ee42dc70db35e7e0aebd73793a806afccb86b30acecb8fe9d024e06bb3fd154c678926d884df3ae696c71adcbf1339a5762e19c4d@testnet-bootnodes.hsk.xyz:30303,enode://dba82c6b384844a00a54ecdfcb34c209ea714072558db80512d4c65e760846d054cf3f58a826cba33b6b410498559b7e41b147dfa487f8cba3d25d2b5bb9e7bc@testnet-bootnodes.hsk.xyz:30304
+      - --cache=${HASHKEYCHAIN_TESTNET_OP_GETH_PRUNED_PEBBLE_PATH_CACHE:-1024}
       - --datadir=/data
       - --db.engine=pebble
       - --gcmode=full