dBFT: ensure WatchOnly is able to properly handle threshold block signing scheme

[AnnaShaleva]

In the end, there's no functional changes in fact. But decryption is checked and threshold signatures work us expected even for WatchOnly node that only has a shared PublicKey available. Here's an example of logs for WatchOnly after NeoXAMEV fork is enabled.

INFO [12-05|17:55:38.335] New block in the chain                   "dbft index"=7 "chain index"=7 hash=0x60ed240da6d7ce0a03be82f301bd0a542e93dea2f2afb2774b78a06ee942a25c "parent hash"=0x3a0e950908b4cc4ff45c904ba5d49bbeaca1a136d7fcdd661ce923369ee7e723 primary=0 coinbase=0x1212000000000000000000000000000000000003 "mix digest"=0x719da1d566c38df3e89e79147d284a26cee6355b89071ba58af7caac0882d38b
INFO [12-05|17:55:38.335] Fetching latest sealing proposal         "desired number"=8
INFO [12-05|17:55:38.335] Commit new sealing work                  number=8 sealhash=b9f016..1ae838 "parent hash"=60ed24..42a25c etherbase=0x1212000000000000000000000000000000000003 txs=1 gas=30000 fees=0.0006 elapsed="511.766µs"
INFO [12-05|17:55:39.335] Sealing proposal updated                 number=8 sealhash=b9f016..1ae838 "parent hash"=60ed24..42a25c txs=1
2024-12-05T17:55:39.337+0300	INFO	[email protected]/dbft.go:112	initializing dbft	{"height": 8, "view": 0, "index": -1, "role": "WatchOnly"}
...
2024-12-05T17:55:48.388+0300	INFO	[email protected]/dbft.go:545	received PreCommit	{"validator": 0}
2024-12-05T17:55:48.390+0300	INFO	[email protected]/check.go:66	processing PreBlock	{"height": 8, "view": 0, "tx_count": 1, "preCommit_count": 5}
INFO [12-05|17:55:48.396] Envelope data decrypted                  "envelope hash"=5312be..a52d44 "envelope index"=0 data=f869808509502f90008252089474f4effb0b538baec703346b03b6d9292f53a4cd0180850113a4538ea09f03664a56ae11cd9cfb5efedc1648c374d51ae91982f7b836893383e4c52f0aa067c4771d614d7c296aecddfd25aae6fab3276e8a48114f87953b5c03c75bad76
...
2024-12-05T17:55:48.411+0300	INFO	[email protected]/dbft.go:595	received Commit	{"validator": 5}
2024-12-05T17:55:48.411+0300	DEBUG	[email protected]/check.go:111	not enough to commit	{"count": 4}
2024-12-05T17:55:48.411+0300	DEBUG	[email protected]/dbft.go:231	received message	{"type": "Commit", "from": 2, "height": 8, "view": 0, "my_height": 8, "my_view": 0}
2024-12-05T17:55:48.412+0300	INFO	[email protected]/dbft.go:595	received Commit	{"validator": 2}
2024-12-05T17:55:48.412+0300	INFO	[email protected]/check.go:118	approving block	{"height": 8, "hash": "0xeaf0019b9b518c2fc82f5c597c9dd37c6292f1b730bd5ac5b56454bb6ffec10c", "tx_count": 1, "merkle": "0x245bb90704b3b326b1fe937cf6b726630a3e7e41caf516c8a99b5a9483f925d0", "prev": "0x60ed240da6d7ce0a03be82f301bd0a542e93dea2f2afb2774b78a06ee942a25c"}
INFO [12-05|17:55:48.472] Successfully wrote new block with state  number=8 hash=d457e2..5c030b
INFO [12-05|17:55:48.473] New block in the chain                   "dbft index"=8 "chain index"=8 hash=0xd457e2ebb8bea29a378c5c383b567c914430b171800d191f63bb6808235c030b "parent hash"=0x60ed240da6d7ce0a03be82f301bd0a542e93dea2f2afb2774b78a06ee942a25c primary=1 coinbase=0x1212000000000000000000000000000000000003 "mix digest"=0x719da1d566c38df3e89e79147d284a26cee6355b89071ba58af7caac0882d38b
INFO [12-05|17:55:48.473] Fetching latest sealing proposal         "desired number"=9

@txhsl, please, take a look, this PR will be useful for #332 testing. I generated antimev keystore for WatchOnly node and setup it manually (if needed, then I can share the code, it's based on our TPKE tests), so that WatchOnly keystore doesn't have private key share, and only has access to global public key.

[txhsl]

Seems good, but I have to replace the new keystore file in #332, and change the privnet genesis a bit.