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/op-mainnet-op-geth-pruned-pebble-path--fireeth.yml

@@ -59,6 +59,7 @@ services:
       - GETH_ROLLUP_SEQUENCERHTTP=https://mainnet-sequencer.optimism.io
     entrypoint: [sh, -c, exec fireeth start reader-node --reader-node-arguments "$*", _]
     command:
+      - --cache=${OP_MAINNET_OP_GETH_PRUNED_PEBBLE_PATH_CACHE:-1024}
       - --datadir=/data
       - --db.engine=pebble
       - --gcmode=full