eth/filters: add global block logs cache

[s1na]

This adds a cache for block logs which is shared by all filters. In order to share the cache reference, filters now need to be created through a 'filter system' object. Cache size is user-configurable via --cache.blocklogs.

This PR is an alternative to #25425.
cc @ryanschneider

Fixes #25421
Includes #25468, which should be merged first.

[ryanschneider]

lgtm! Thanks!

[holiman]

LGTM

[rjl493456442]

It's weird to add this "duplicated" check here, usually a nil error means the returned result is not empty.

I would vote to add the check here https://github.com/ethereum/go-ethereum/pull/25459/files#diff-9886da3412b43831145f62cec6e895eb3613a175b945e5b026543b7463454603R204

func (b *EthAPIBackend) GetLogs(ctx context.Context, hash common.Hash) ([][]*types.Log, error) {
       result := b.eth.blockchain.GetLogsByHash(hash)
       if result == nil {
             return nil, errors.New("xxx")
       }
       return b.eth.blockchain.GetLogsByHash(hash), nil
}

Also in les_apiBackend.GetLogs, we should also return the error if logs is not found.

func (b *LesApiBackend) GetLogs(ctx context.Context, hash common.Hash) ([][]*types.Log, error) {
	if number := rawdb.ReadHeaderNumber(b.eth.chainDb, hash); number != nil {
		return light.GetBlockLogs(ctx, b.eth.odr, hash, *number)
	}
	return nil, fmt.Errorf("failed to get logs for block %x", hash)
}

[fjl]

This is ready for testing now. The cache size is configurable via --cache.logcache or in TOML with Eth.FilterLogCacheSize = 128, for example.

@holiman Please re-check this, the PR has changed significantly after your initial review.