Improve security and performance (fix #12)

[DIP72]

Overview:

This pull request resolves Issue #12 by addressing multiple performance, validation, and reliability concerns in the EasyWiFi library.

Changes Made:

1. Removed delay(2000) and implemented a non-blocking timing mechanism using millis() for smoother task handling.
2. Added proper SSID and password validation to prevent invalid credentials from being saved.
3. Implemented explicit checks and user feedback for credential save failures.
4. Modified server and dnsServer usage to avoid conflicts when multiple EasyWiFi instances are created.
5. Introduced a watchdog/timeout feature to prevent the device from getting stuck in captive portal mode.

Impact:

These updates enhance the stability, security, and user experience of the EasyWiFi library by improving responsiveness and reducing potential runtime issues.

Note:

Fixes #12
Please review the changes and merge if they meet the project standards