Fix: Isolate SetThreadExecutionState modes on same thread from each other

[fohrloop]

Fixes: #167

The SetThreadExecutionState Method may now have multiple modes (same or different) activated within the same python thread without them interfering with each other on activation or deactivation, as wakepy creates a separate worker thread for the single purpose of setting and keeping the thread execution flag each time you activate a mode with the SetThreadExecutionState wakepy.Method.

Before this PR

Running

from wakepy import keep
import time 

def foo():
   with keep.running():
       ...

with keep.presenting():
    foo()
    time.sleep(1000)

produced no lock holders (Expected: DISPLAY and SYSTEM):

PS C:\Users\niko> powercfg /requests
DISPLAY:
None.

SYSTEM:
None.

AWAYMODE:
None.

EXECUTION:
None.

PERFBOOST:
None.

ACTIVELOCKSCREEN:
None.

After this PR

Running

from wakepy import keep
import time 

def foo():
   with keep.running():
       ...

with keep.presenting():
    foo()
    time.sleep(1000)

produces (as expected)

PS C:\Users\niko> powercfg /requests
DISPLAY:
[PROCESS] \Device\HarddiskVolume3\Python310\python.exe

SYSTEM:
[PROCESS] \Device\HarddiskVolume3\Python310\python.exe

AWAYMODE:
None.

EXECUTION:
None.

PERFBOOST:
None.

ACTIVELOCKSCREEN:
None.

(DISPLAY and SYSTEM kept awake as expected), and running

def foo():
   with keep.presenting():
       ...

with keep.running():
    foo()
    time.sleep(1000)

produces:

PS C:\Users\niko> powercfg /requests
DISPLAY:
None.

SYSTEM:
[PROCESS] \Device\HarddiskVolume3\Python310\python.exe

AWAYMODE:
None.

EXECUTION:
None.

PERFBOOST:
None.

ACTIVELOCKSCREEN:
None.

(only SYSTEM kept awake as expected)