Fix channel close behavior in Multicast when done without error

Move emission struct inside Delay function

Rename Connect type to Connector for clarity

Add subscription tests with context and timeout scenarios

Refactor Do and Finally to use Tap with observers

Rename package from x to rx

The package has been renamed from 'x' to 'rx' to better reflect its purpose as a reactive programming library for Go. Updated all imports and documentation accordingly.

Upgrade minimum go version to 1.16 and upgrade dependencies

Fix some test cases that broke