uwb: Refactor default AIDL HAL implementation

Refactor the implementation in order to:
  - simplify the code and make it less error prone
    by keeping the serial open at all times
  - address issues about futures being awoken too often
    taking CPU time

Bug: 345676140
Test: m android.hardware.uwb-service
Test: atest CtsUwbTestCases
Test: AVD boot test
Change-Id: Ibe4f00dab87ffac42f627def5ca84c0be5147820