Add wrong-XMR amount regression test

[louiss72]

Summary

• add a second integration test for the wrong-XMR-amount path
• verify Bob transitions into WaitingForCancelTimelockExpiration after Alice under-locks Monero instead of continuing toward Bitcoin redeem
• keep the existing refund/resume test intact while adding a more direct assertion for the behavior requested in [0.5 XMR] Integration test where Alice locks wrong amount #828

Verification

• git diff --check
• cargo test -p swap bob_refunds_when_xmr_amount_is_not_exact could not be run locally because this environment does not have cargo or rustc

Notes

• the repo already had coverage for the eventual refund path after Bob resumes from DB
• this change adds the earlier-state regression check that Bob waits for the cancel timelock once the Monero amount is wrong, before any redeem path is allowed

Fixes #828

Preferred payout asset if accepted: XMR.

[Einliterflasche]

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