* fix(drand): `StateGetBeaconEntry` uses chain beacons for historical epochs
Fixes: https://github.com/filecoin-project/lotus/issues/12414
Previously StateGetBeaconEntry would always try and use a drand beacon to get
the appropriate round. But as drand has shut down old beacons and we've
removed client details from Lotus, it has stopped working for historical
beacons.
This fix restores historical beacon entries by using the on-chain lookup,
however it now follows the rules used by StateGetRandomnessFromBeacon and the
get_beacon_randomness syscall which has some quirks with null rounds prior to
nv14. See https://github.com/filecoin-project/lotus/issues/12414#issuecomment-2320034935
for specifics.
StateGetBeaconEntry still blocks for future epochs and uses live drand beacon
clients to wait for and fetch rounds as they are available.
* fixup! fix(drand): `StateGetBeaconEntry` uses chain beacons for historical epochs
* fixup! fix(drand): `StateGetBeaconEntry` uses chain beacons for historical epochs
