Improve unknown coin selection algorithm error message

[yashithac618]

Description

Improve the error message returned when an unknown coin selection algorithm is provided.

Previously, the error message only displayed:

unknown coin selection algorithm '{unknown}'

This change updates the message to clearly list the supported algorithms:

unknown coin selection algorithm ''. Supported algorithms: largest-first, s

Notes to the reviewers

This change only modifies the error message in the FromStr implementation of CoinSelectionAlgo.
No logic or behavior has been changed.

Changelog notice

Improved CLI error message for invalid coin selection algorithm input.

Checklists

All Submissions:

• I followed the contribution guidelines

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

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