Cantina fixes reviews to main

[atacann]

Apply review comments of cantina fixes

[Copilot]

Pull Request Overview

This PR applies review comments from a Cantina security audit, focusing on bug fixes and improvements identified during the review process.

• Added a missing call to disprove_if_ready in the kickoff state machine
• Fixed fee rate calculation to prevent division precision issues
• Improved watchtower uniqueness check to use getter methods

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
core/src/states/kickoff.rs	Added missing disprove_if_ready call in state machine logic
core/src/extended_bitcoin_rpc.rs	Fixed fee rate calculation to prevent precision loss from division
core/src/deposit.rs	Updated watchtower uniqueness check to use consistent getter methods
core/src/builder/transaction/operator_collateral.rs	Added MIN_TAPROOT_AMOUNT import and updated condition for standard transactions

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