Add explicit sync and asyncio APIs

[jacobtomlinson]

Closes #39

kr8s uses asyncio under the hood by default. This PR changes the public API to be sync by default. In order to support a sync API this PR:

• Moves all library code into private submodules (objects.py => _objects.py, portforward.py => _portforward.py).
• Expose all public code via kr8s.asyncio so that asyncio is available but opt-in.
• Vendored in universalasync and modified to be opt-in only (it was only 100 lines or so and was hard to import and subclass without rewriting the whole thing).
• Expose classes like Api and all objects including Pod, Service, etc with the universalasync wrapper.
• Rename all object methods to be private (Pod.ready() => Pod._ready(), etc) and replace with new public method that awaits the private one.
  • This allows a method to call other methods with await regardless of the univeralasync wrapper.
• Added nest-asyncio to allow the sync API to be used within a running event loop (Jupyter is a common case where users may not know there is an event loop running).

Sync API

import kr8s

api = kr8s.api()
pods = api.get("pods")  # Return Pod objects also are sync

for pod in pods:
    assert pod.exists()

Asyncio API

import kr8s.asyncio

api = kr8s.asyncio.api()
pods = await api.get("pods")  # Returned Pod objects are also asyncio

for pod in pods:
    assert await pod.exists()

[codecov]

Codecov Report

Merging #40 (99d5fde) into main (b1331f9) will decrease coverage by 0.60%.
The diff coverage is 95.37%.

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
- Coverage   97.33%   96.73%   -0.60%     
==========================================
  Files          15       21       +6     
  Lines        1236     1562     +326     
==========================================
+ Hits         1203     1511     +308     
- Misses         33       51      +18     

Impacted Files	Coverage Δ
kr8s/tests/test_objects.py	97.64% <84.21%> (-2.36%)	⬇️
kr8s/_asyncio.py	90.90% <90.90%> (ø)
kr8s/tests/test_api.py	99.00% <94.11%> (-1.00%)	⬇️
kr8s/_portforward.py	94.17% <94.17%> (ø)
kr8s/_objects.py	94.81% <94.81%> (ø)
kr8s/__init__.py	100.00% <100.00%> (ø)
kr8s/_api.py	98.46% <100.00%> (-0.04%)	⬇️
kr8s/asyncio/__init__.py	100.00% <100.00%> (ø)
kr8s/asyncio/objects.py	100.00% <100.00%> (ø)
kr8s/asyncio/portforward.py	100.00% <100.00%> (ø)
... and 4 more