Drop sniffio and improved limetime

[almarklein]

• add rendercanvas.get_running_loop() that returns the running loop for the current thread.
• Instead of sniffio use asyncgen_hooks to detect the current framework.
• The asyncadapter still registers with sniffio, if sniffio can be imported, to remain compatibility for libs that use sniffio.
• Some more improvements to the loop lifecycle.

---

I ran some benchmarks

import sys
import time
import threading
import sniffio

n = 1000000


#

t0 = time.perf_counter()
for _ in range(n):
    try:
        sniffio.current_async_library()
    except sniffio.AsyncLibraryNotFoundError:
        pass
t1 = time.perf_counter()
print(' sniffio:', t1 - t0)


#

def detect_current_async_lib():
    ob = sys.get_asyncgen_hooks()[0]
    if ob is not None:
        try:
            libname = ob.__module__.partition(".")[0]
        except AttributeError:
            return None
        if libname == "rendercanvas":
            libname = "rendercanvas.utils.asyncadapter"
        return libname


t0 = time.perf_counter()
for _ in range(n):
    detect_current_async_lib()
t1 = time.perf_counter()
print('asyncgen:', t1 - t0)

This shows that using asyncgen_hooks is faster. It's speed is also more stable than sniffio, which speed depends on the order it tries different libs.

[almarklein]

I'm so done with these loops ...

[almarklein]

Ref pygfx/wgpu-py#780, don't need the idea of a running loop anymore. So this now boils down to dropping sniffio (using async_gen_hooks instead) and some tweaks to improve the definition of when a loop is running.