Optimise gas use for `ExtendSectorExpiration2`

_(Moved from https://github.com/filecoin-project/builtin-actors/issues/1598#issuecomment-2652810696 after I realised we're talking about a slightly different thing, I jumped the gun)._

Yesterday someone was asking about gas usage of "sector extensions or recoveries". I had a quick look at some example messages for `ExtendSectorExpiration2`, which involved verified claims, and came to the conclusion that we should absolutely look at optimising them for that case at least.

[bafy2bzaceaqaxndnsczslx3cx35q6tluaisidgs36ipxsemksaqafehlcifuy](https://filfox.info/en/message/bafy2bzaceaqaxndnsczslx3cx35q6tluaisidgs36ipxsemksaqafehlcifuy?t=4) is one such message:

* 402 separate calls to verifreg [here](https://github.com/filecoin-project/builtin-actors/blob/5aad41bfa29d8eab78f91eb5c82a03466c6062d2/actors/miner/src/lib.rs#L3712)
* 33% of the gas is spent in the miner actor, the majority being storage gas writing new sector infos out which is understandable.
* The rest is divided by 402, so it's lots of small cuts from executing wasm.

They all look like some variation of this:

```
Subcall (f02301➜f06) gas charges:
┌───────────────────────┬───────┬─────────────┬────────┬─────────────┬────────┬───────────┬────────┐
│ Type │ Count │ Storage Gas │ S% │ Compute Gas │ C% │ Total Gas │ T% │
├───────────────────────┼───────┼─────────────┼────────┼─────────────┼────────┼───────────┼────────┤
│ OnActorGetRoot │ 1 │ 0 │ 0.00 │ 300 │ 0.01 │ 300 │ 0.00 │
│ OnBlockCreate │ 1 │ 662 │ 0.05 │ 209 │ 0.00 │ 871 │ 0.01 │
│ OnBlockOpen │ 7 │ 67320 │ 4.88 │ 48900 │ 0.91 │ 116220 │ 1.72 │
│ OnBlockOpenBase │ 7 │ 1312080 │ 95.07 │ 2100 │ 0.04 │ 1314180 │ 19.50 │
│ OnBlockRead │ 8 │ 0 │ 0.00 │ 4656 │ 0.09 │ 4656 │ 0.07 │
│ OnBlockStat │ 1 │ 0 │ 0.00 │ 0 │ 0.00 │ 0 │ 0.00 │
│ OnGetActorCodeCid │ 1 │ 0 │ 0.00 │ 0 │ 0.00 │ 0 │ 0.00 │
│ OnGetBuiltinActorType │ 1 │ 0 │ 0.00 │ 0 │ 0.00 │ 0 │ 0.00 │
│ OnHashing │ 2 │ 0 │ 0.00 │ 42 │ 0.00 │ 42 │ 0.00 │
│ OnMessageContext │ 1 │ 0 │ 0.00 │ 0 │ 0.00 │ 0 │ 0.00 │
│ OnMethodInvocation │ 1 │ 0 │ 0.00 │ 75000 │ 1.40 │ 75000 │ 1.11 │
│ OnReturnValue │ 1 │ 0 │ 0.00 │ 0 │ 0.00 │ 0 │ 0.00 │
│ OnScanIpldLinks │ 8 │ 0 │ 0.00 │ 114815 │ 2.14 │ 114815 │ 1.70 │
│ OnSyscall │ 24 │ 0 │ 0.00 │ 336000 │ 6.27 │ 336000 │ 4.99 │
│ wasm_exec │ 26 │ 0 │ 0.00 │ 4304317 │ 80.33 │ 4304317 │ 63.88 │
│ wasm_memory_grow │ 1 │ 0 │ 0.00 │ 26215 │ 0.49 │ 26215 │ 0.39 │
│ wasm_memory_init │ 1 │ 0 │ 0.00 │ 445645 │ 8.32 │ 445645 │ 6.61 │
│ Total │ 92 │ 1380062 │ 100.00 │ 5358199 │ 100.00 │ 6738261 │ 100.00 │
└───────────────────────┴───────┴─────────────┴────────┴─────────────┴────────┴───────────┴────────┘
```

https://github.com/filecoin-project/ref-fvm/issues/2102 is related to this, there's likely ways to reduce that call cost. But what we really should be doing is batching these calls outside of that inner per-sector loop.