Try to use metabase transaction context

One of the problems with the metabase is excessive convertions of addresses/CID/OIDs to use as keys or bucket names.
The cost is non-negligible as can be seen from the benchmarks (will provide them shortly).

Describe the solution you'd like

Introduce tx-level cache containing the most frequently used values.
Converting some items to string can be done outside of the transaction, we also can reuse the same slice for creating bucket names.

type txContext struct {
    tx *bbolt.Tx
   addr string
   cid string
   oid string
   bucketName []byte // preallocated bucket name
}

I have benched similar thing once, while trying it with pebble backend #619 , the result was positive. I think similar benefits are applicable to bolt.

Start by locating the metabase implementation and its bbolt transaction paths, then review issue #619 for prior Pebble context. Define completion around measuring whether a transaction-level cache reduces conversions and reuses bucket-name storage, with benchmarks supplied for comparison.