feat(wip): sub 1 sat fee

[reez]

Description

Test support for sub 1 sat fees.

Notes to the reviewers

FeeRate supports https://docs.rs/bitcoin-units/0.1.2/bitcoin_units/fee_rate/struct.FeeRate.html

Needed to update a method in BDKService.

(hardcoded fee for testing)

If I did 0.5, I got sendrawtransaction RPC error: {"code":-26,"message":"min relay fee not met, 72 < 142"}

So then I went to 0.99 (worked but is within current policy so not surprising) https://mempool.space/testnet4//tx/fa7e423f5cdebf1b1d5c1efa67aaed4350ec0fb6347200398f4f678b9256957f

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I have formatted my code with swift-format per .swift-format file

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• UI changes tested on small, medium, and large devices to ensure layout consistency

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

[reez]

On the last screen of send flow it would be nice to show fee rate (already show fee in sats), especially for this sort of thing