Fix/reset polkadot proxy account nonce

[ramizhasan111]

Pull Request

Closes: PRO-864

Checklist

Please conduct a thorough self-review before opening the PR.

• I am confident that the code works.
• I have updated documentation where appropriate.

Summary

the resetting of the polkadot proxy account nonce is now moved to when the polkadot rotation tx is constructed.

[linear]

PRO-864 Polkadot Vault nonce sync issues

On Perseverance, the vault nonce got out of sync. The current signer key is unavailable, because we fail to broadcast the vault rotation transaction. That is because it uses the wrong nonce.

The handover transaction was constructed in statechain block 363820 with nonce 0

The signing key is da5ebeaf4401c7f3c627c0a91d1858ddde7dcc5a10ea585185e7d182f1d9d72a

But nonce 0 for that key had already been used by a different transaction that was submitted in statechain block 361716 (and made it into polkadot in polkadot block 382499)

The account nonce was reset from 2 to 0 in statechain block 361702. Even after that, several attempts to sign/submit extrinsics using nonce 2 were made

I believe the underlying cause was that a swap drained the entire dot vault, which prevented the transaction from going through. once we provided additional funds, the transaction succeeded, but by that time our nonce counting somehow got out of sync

[codecov]

Codecov Report

Merging #4053 (b91c06c) into release/0.9 (0fbf186) will decrease coverage by 0%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           release/0.9   #4053   +/-   ##
===========================================
- Coverage           72%     72%   -0%     
===========================================
  Files              366     366           
  Lines            56871   56864    -7     
  Branches         56871   56864    -7     
===========================================
- Hits             41031   41006   -25     
- Misses           13759   13770   +11     
- Partials          2081    2088    +7     

Files	Coverage Δ
state-chain/chains/src/dot.rs	41% <ø> (ø)
state-chain/pallets/cf-vaults/src/lib.rs	79% <ø> (-<1%)	⬇️
state-chain/pallets/cf-vaults/src/mock.rs	82% <ø> (-<1%)	⬇️
state-chain/runtime/src/lib.rs	39% <ø> (ø)
state-chain/traits/src/lib.rs	52% <ø> (-<1%)	⬇️
state-chain/runtime/src/chainflip.rs	42% <0%> (-1%)	⬇️
state-chain/chains/src/dot/api.rs	1% <0%> (-<1%)	⬇️
state-chain/pallets/cf-environment/src/lib.rs	67% <0%> (-3%)	⬇️

... and 3 files with indirect coverage changes

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[dandanlen]

I'll cherry-pick this into the 0.9.3 branch.

[dandanlen]

Closing this here, will cherry pick from main via a separate PR.