Move introspection APIs into trio.hazmat

[njsmith]

See #317

[codecov]

Codecov Report

Merging #325 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #325      +/-   ##
==========================================
- Coverage   99.24%   99.08%   -0.16%     
==========================================
  Files          86       86              
  Lines       10327    10739     +412     
  Branches      726      782      +56     
==========================================
+ Hits        10249    10641     +392     
- Misses         61       71      +10     
- Partials       17       27      +10

Impacted Files	Coverage Δ
trio/_toplevel_core_reexports.py	100% <ø> (ø)	⬆️
trio/hazmat.py	100% <ø> (ø)	⬆️
trio/__init__.py	100% <ø> (ø)	⬆️
trio/_socket.py	96.28% <0%> (-3.72%)	⬇️
trio/tests/test_socket.py	99.38% <0%> (-0.62%)	⬇️
trio/tests/test_highlevel_open_tcp_stream.py	100% <0%> (ø)	⬆️
trio/_abc.py	100% <0%> (ø)	⬆️
trio/tests/test_highlevel_socket.py	100% <0%> (ø)	⬆️
trio/tests/test_highlevel_open_tcp_listeners.py	100% <0%> (ø)	⬆️

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[njsmith]

Coverage changes appear to be spurious, due to #326 being merged in between the Linux/Windows builds and the MacOS builds.