Use EthHash compatible type for subscription and filter IDs

[iand]

Related Issues

Fixes filecoin-project/ref-fvm#1189 and filecoin-project/ref-fvm#1208

Fixes some itest breakage introduced around 23007b0

Proposed Changes

Uses 32 byte arrays for subscriiption and filter ids, populated from a 16 byte uuid which should be good enough randomness.

Additional Info

Checklist

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[arajasek]

Would the following refactor be possible:

• Move the new FilterID type to chain/types/event.go
• Have the API use FilterID instead of EthFilterID
• Drop EthFilterID entirely?

[arajasek]

Suggested change

	copy(id[:], rawid[:]) // uuid is 16 bytes
	copy(id[:], rawid) // uuid is 16 bytes, the last 16 bytes are zeroed

[iand]

• Move the new FilterID type to chain/types/event.go
• Have the API use FilterID instead of EthFilterID

Yes to these two

• Drop EthFilterID entirely?

We need to keep this to preserve the Ethereum specific json marshalling

[iand]

@arajasek PTAL

[arajasek]

LGTM