fix(windows): retry transient GATT discovery failures

[usmanmehmood55]

Summary

This PR improves Windows BLE connections made immediately after device discovery. Windows can transiently report GATT services as Unreachable while establishing the underlying connection, causing the first attempt to fail even though the device is available.

Changes

• Retry uncached GATT service discovery when Windows temporarily reports Unreachable.
• Keep the retry bounded to two additional attempts with a short progressive delay.
• Retry only transient reachability failures. Authorization and protocol errors still fail immediately.
• Avoid using cached services as evidence of a live connection.
• Map native Windows connection failures to the corresponding Dart error codes.
• Match only exact Windows callback messages to avoid misclassifying unrelated errors.
• Add unit coverage for unreachable devices, missing devices, access denial, protocol errors, and unrelated messages.
• Add a Windows HIL scenario covering 20 repeated scan, immediate connection, service-discovery, and GATT-read cycles.
• Document the behavior change in the changelog.

Validation

• flutter analyze passed.
• flutter test passed with 114 tests.
• Windows release build completed successfully.
• Hardware-in-loop tests, as well as manual testing