fix(wallet): fix SingleRandomDraw to error if insufficient funds

[notmandatory]

Description

• fix SingleRandomDraw to error if insufficient funds
• fixed spelling and clippy errors (see: Allow custom fallback algorithm for bnb #1581 (comment))
• updated tests to check for error variant instead of a panic

Notes to the reviewers

Since the single random draw algo can be used on its own it needs to be able to return an insufficient funds error. I think the reason we didn't catch this before is that single random draw already check for sufficient required + optional utxo amounts and returns the insufficient funds error.

Changelog notice

• fix SingleRandomDraw coin selection to error if there are insufficient funds for a requested payment amount.

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

[ValuedMammal]

ACK 22a2f83