Silent errors / warnings occur when building docs

Description of issue

When building the docs, there are errors and warnings that only show up if passing the verbose (-v) argument to sphinxbuild.

1. viewcode import errors
   We get errors like

ModuleNotFoundError: No module named 'niscope.Session'
viewcode can't import niscope.Session, failed with error "No module named 'niscope.Session'"

This is because we are incorrectly setting .. py:currentmodule:: ${module_name}.Session in class.rst. Session is a class, not a module.
It should be .. py:currentmodule:: ${module_name}.session.

In nitclk, we are sometimes incorrectly setting .. py:currentmodule:: ${module_name}. This needs .session appended to it.
Other times, we are setting .. py:currentmodule:: ${module_name}.SessionReference, which needs SessionReference to become session.

After fixing this, other problems are revealed.

2. Methods aren't being found

reading sources... [100%] niscope/class
Didn't find abort in niscope.session
Didn't find acquisition_status in niscope.session
Didn't find add_waveform_processing in niscope.session
...

This can be fixed by specifying the class to which the method belongs.
Example:

.. py:method:: abort() becomes .. py:method:: Session.abort()

3. Attributes aren't being found

Didn't find absolute_sample_clock_offset in niscope.session
Didn't find acquisition_start_time in niscope.session
Didn't find acquisition_type in niscope.session
...

I could not determine how to fix this.

Steps to reproduce issue

1. In tox.ini, change docs: sphinx-build -b html -d {envtmpdir}/doctrees . ../generated/docs/html {posargs} to docs: sphinx-build -v -b html -d {envtmpdir}/doctrees . ../generated/docs/html {posargs}
2. Run tox -e clean
3. Run tox -e codegen
4. Run tox -e docs

You will see the issues mentioned above.

Start with the verbose docs-build commands in tox.ini, then inspect the generated class.rst files and the nitclk directives that set py:currentmodule. Correct the module and method references described in the issue, and investigate the unresolved attribute warnings. Run tox -e clean, tox -e codegen, and tox -e docs; done means the documented viewcode, method, and attribute warnings are addressed.