feat: pool fills rpc subscription

[msgmaxim]

Pull Request

Closes: PRO-1543

Checklist

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

• [x] I am confident that the code works.
• [ ] I have written sufficient tests.

Summary

• Moved most of the logic from order_fills lp-api command under custom-rpc so that it can be used/imported in both places.

• Added the ability to new_subscription to pass state from one call of the closure to the next (needed to pass previous pool state in this case, but this could be useful in other subscriptions too).

• Added new api methods to runtime: cf_pools and cf_lp_events; limited events to LP only to minimise any compatibility issues between runtime and node. The order updates are computed outside of runtime since they require querying (or caching) previous state of the pools storage item (not sure if this can be done from within runtime directly).

• Tested on localnet with wscat -c ws://localhost:9944 followed by {"id":1, "jsonrpc":"2.0", "method": "cf_subscribe_lp_order_fills"} and performing some swaps.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0.81967% with 242 lines in your changes missing coverage. Please review.

Project coverage is 70%. Comparing base (70f0440) to head (9d22d36). Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
state-chain/custom-rpc/src/order_fills.rs	0%	121 Missing :warning:
state-chain/custom-rpc/src/lib.rs	0%	107 Missing :warning:
state-chain/runtime/src/lib.rs	0%	0 Missing and 13 partials :warning:
state-chain/pallets/cf-pools/src/lib.rs	50%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5214 +/- ## ====================================== - Coverage 70% 70% -0% ====================================== Files 486 487 +1 Lines 86515 86597 +82 Branches 86515 86597 +82 ====================================== - Hits 60771 60567 -204 - Misses 22425 22692 +267 - Partials 3319 3338 +19 ```

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[dandanlen]

@msgmaxim i've added the capability to query storage directly and reverted the change to cf-pools. Let me know what you think.

[msgmaxim]

@msgmaxim i've added the capability to query storage directly and reverted the change to cf-pools. Let me know what you think.

Looks good. Thanks! Let me know if this can be merged (or happy for you to do so).

[dandanlen]

Cool - think I'll rebase it (39 commits behind main) and let CI run once more before merging.

[msgmaxim]

I'm asking @j4m1ef0rd to approve this so it can be merged.