Feat: charging broker fee per chunk and in USDC

[msgmaxim]

Pull Request

Closes: PRO-1540 and PRO-1483

Checklist

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

• [x] I am confident that the code works.
• [x] I have written sufficient tests.
• [ ] I have written and tested required migrations.
• [ ] I have updated documentation where appropriate.

Summary

The PR is indended to be reviewed by individual commits

• Broker fee now behaves exactly like network fee, charged at the same time (once we have intermediate amount) and in USDC.
• Moved broker_fee field from SwapRequested to SwapExecuted (FYI @zoheb391 and @acdibble). Don't think there are any other implications for the product, other than brokers noticing that only their USDC balance is changing.
• Updated tests; swap_broker_fee_subtracted_from_swap_amount was mostly a duplicate so I merged it with expect_earned_fees_to_be_recorded.
• Also, as discussed, combined Ccm and Regular variants from SwapRequestState into UserSwap. Didn't really result in code deduplication, but at least we no longer repeat swap parameters (like the newly added broker_fees).

Edit: Updated broker fee tests in bouncer. Because all fees are charged in USDC I ended up leaving only a test for one asset (as opposed to all assets). Keeping all assets seems no longer necessary, and wouldn't be trivial (would likely require running the tests sequentially or with multiple broker account).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 92.98246% with 28 lines in your changes missing coverage. Please review.

Project coverage is 70%. Comparing base (fb4385c) to head (03a5c06). Report is 3 commits behind head on main.

Files	Patch %	Lines
state-chain/pallets/cf-swapping/src/lib.rs	88%	21 Missing and 5 partials :warning:
state-chain/pallets/cf-swapping/src/tests.rs	99%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5161 +/- ## ====================================== - Coverage 70% 70% -0% ====================================== Files 481 481 Lines 85760 85829 +69 Branches 85760 85829 +69 ====================================== - Hits 60207 60106 -101 - Misses 22286 22452 +166 - Partials 3267 3271 +4 ```

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