Filter duplicate coins before coin selection

[evanlinjin]

Fixes #1240

Description

We now filter out duplicate coins before calling CoinSelectionAlgorithm::coin_select. If a UTXO exists in both required_utxos and optional_utxos, only the copy in required_utxos will be kept.

Test helper methods are also updated to not create duplicate UTXOs.

Changelog notice

Fixed

• Filter out duplicate UTXOs before calling CoinSelectionAlgorithm::coin_select. If a UTXO exists in both required_utxos and optional_utxos, only the copy in required_utxos will be kept.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

Bugfixes:

* [ ] This pull request breaks the existing API

• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[LLFourn]

Can't we just fix this before passing it in rather than change every coin selection algorithm?

[evanlinjin]

Can't we just fix this before passing it in rather than change every coin selection algorithm?

That's a good point. I assumed that people will use the trait directly. If we assume that people will always go through the TxBuilder what you suggested is better.

[LLFourn]

I don't think anyone is using these directly so I'd go for the more succinct fix.

[danielabrozzoni]

utACK 5299db3