enhancement: reuse existing invoices for order payments in POS

[ajaysehwal]

Description

Relates to issue: **ZEUS-#3045

Please enter a description and screenshots, if appropriate, of the work covered in this PR

These changes fix the issue where a new invoice is created every time an order is paid, even if a valid invoice already exists. Now the system will check for existing invoices and reuse them if they are still valid, Improving efficiency and reducing unnecessary invoice creation.

This pull request is categorized as a:

• [x] New feature
• [ ] Bug fix
• [x] Code refactor
• [ ] Configuration change
• [ ] Locales update
• [ ] Quality assurance
• [ ] Other

Checklist

• [x] I’ve run yarn run tsc and made sure my code compiles correctly
• [x] I’ve run yarn run lint and made sure my code didn’t contain any problematic patterns
• [x] I’ve run yarn run prettier and made sure my code is formatted correctly
• [x] I’ve run yarn run test and made sure all of the tests pass

Testing

If you modified or added a utility file, did you add new unit tests?

• [ ] No, I’m a fool
• [ ] Yes
• [x] N/A

I have tested this PR on the following platforms (please specify OS version and phone model/VM):

• [ ] Android
• [x] iOS

I have tested this PR with the following types of nodes (please specify node version and API version where appropriate):

• [ ] Embedded LND
• [ ] LND (REST)
• [ ] LND (Lightning Node Connect)
• [ ] Core Lightning (CLNRest)
• [ ] Nostr Wallet Connect
• [ ] LndHub

Locales

• [ ] I’ve added new locale text that requires translations
• [ ] I’m aware that new translations should be made on the ZEUS Transfix page and not directly to this repo

Third Party Dependencies and Packages

• [ ] Contributors will need to run yarn after this PR is merged in
• [ ] 3rd party dependencies have been modified:
  • verify that package.json and yarn.lock have been properly updated
  • verify that dependencies are installed for both iOS and Android platforms

Other:

• [ ] Changes were made that require an update to the README
• [ ] Changes were made that require an update to onboarding