feat: miner paramfetch: Don't fetch param files when not needed

[magik6k]

Proposed Changes

On lotus-miner nodes with disabled local PoSt / C2 / PR2 no snarks are ever computed, which means that we don't need .param files for anything. This makes node startup much faster, reducing downtime by a lot when restarts are needed.

Additional Info

Checklist

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[magik6k]

(verified on my setup)