feat: New Assertions methods and better usability

[Zubairahmdfaraz]

This PR adds support for custom visibility assertions in the appium-flutter-driver, including: flutter:assertVisible flutter:assertNotVisible flutter:assertTappable flutter:tap flutter:click flutter:getText

These commands allow clients to verify widget visibility and tappability using Flutter finders (key, text, or label) encoded in base64.

All commands have been locally tested and validated using real device scenarios to ensure proper behavior and compatibility with native Flutter widgets. Also updated execute.ts for command handler and better usability.

[Zubairahmdfaraz]

Please let me know if there are any further modifications

[Zubairahmdfaraz]

Added two more commits because ReadMe changes were not being tracked properly by git. Had to do it manually from github.

[KazuCocoa]

Hi @Zubairahmdfaraz, congrats: the Appium project wants to compensate you for this contribution! Please reply to this comment mentioning @jlipps and @KazuCocoa and sharing your OpenCollective account name, so that we can initiate payment! Or let us know if you decline to receive compensation via OpenCollective. Thank you!

[Zubairahmdfaraz]

Hi @jlipps and @KazuCocoa, thank you so much — I’m truly honored! I’m genuinely happy to see my contribution recognized and valued by the Appium community. I’d be delighted to receive the compensation. My OpenCollective account name is zubairahmdfaraz (https://opencollective.com/zubairahmdfaraz). Looking forward to the next steps!