refactor: extract tx broadcast from component and add unit tests

[lucachaco]

Extract tx broadcast code from component and add unit test (pending)

The following cases will be in a separate PR:

Segwit RBTC to Segwit RBTC (Partial funds))

USDT to USDT (Partial funds))

Legacy BTC to Legacy BTC (All funds)

USDT to USDT (All funds)

Motivation and Context

Decouple logic from component to make it easier to test

How Has This Been Tested?

Yes, locally

Types of changes

• [ ] fix: bug fixes, e.g. fix Button color on DarkTheme.
• [ ] feat: new features, e.g. add Snackbar component.
• [x] refactor: code refactor, e.g. new folder structure for components.
• [ ] docs: changes into documentation, e.g. add usage example for Button.
• [ ] test: adding or updating tests, eg unit, snapshot testing.
• [ ] chore: tooling changes, e.g. change circleci config.
• [ ] BREAKING CHANGE: for changes that break existing usage, e.g. change API of a component.

Checklist:

• [ x] My code follows the code style of this project.

• [ ] My change requires a change to the documentation.

• [ ] I have updated the documentation accordingly.

• [ ] Tests for the changes have been added (for bug fixes / features)

• Other information:

• SCREENSHOTS:

[lucachaco]