* all: clean up code with Go 1.24+ in mind
* all: more old go cleanup
* all: even remove rand_fastrand64
* runtime: revert rand changes
* runtime: re-drop rand_fastrand64
These methods were added in Go 1.20 but were missing from TinyGo's
sync.Map implementation, causing compilation failures for code that
uses them.
The implementation follows the same lock-based approach as the rest
of TinyGo's sync.Map.