Please restore chain_id setter (#2376)

[DefiDebauchery]

In #2376, chain_id was added as a setter. This was a cheap but effective cache to avoid constant lookups during txn building, as simple_cache is not currently async.

There was a discussion about adding some validation, but it may have been an accident that @dbfreem removed it in his subsequent commits in #2432 (as I didn't see any comments about it in that PR). To me, it seems better to have this, even if temporary in a v6.0 branch, and improve upon it later (or become obsoleted by an async version of simple_cache)

[dbfreem]

After looking into this for a little while, looks like @kclowes removed this here.

[fselmo]

The simple cache middleware has been asynced, via #2579, and will be out in next release.