## Why this should be merged
See ava-labs/strevm#120. To get bloom filters for a block when the
header doesn't contain the correct bloom because of SAE's delayed
settlement, you need a custom accessor to provide arbitrary bloom.
## How this works
Introduces an optional interface which, if satisfied by
`filters.Backend` implementations, is used to override the Bloom filter
instead of retrieving it from the `types.Header`.
## How this was tested
Existing tests unchanged. Integration test demonstrates calling of the
override method when present.
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Co-authored-by: Arran Schlosberg <me@arranschlosberg.com>
