feat(api): Allow omitting the mount when loading a 96-channel

[SyntaxColoring]

Overview

The 96-Channel Pipette physically occupies both mounts. But a quirk (not ticketed) of our current Python Protocol API is that you need to specify mount="left" or mount="right". This PR fixes that quirk.

Changelog

Before this PR:

• The Python Protocol API's load_instrument() method takes a mount argument that's required to be "left" or "right".
• The documentation says to use "left" if you're loading a 96-Channel.
• The implementation ignores whichever value you pass in; "left" and "right" do the same thing in practice.

With this PR:

• The mount argument is allowed to be omitted or None if you're loading a 96-channel. For all other pipettes, it's still required to be "left" or "right".
• The documentation says to omit mount if you're loading a 96-channel.
• The implementation continues to ignore whichever value you pass in. This is for compatibility with existing protocols.

This is roughly analogous to how we treat the Thermocycler Module, which can only be loaded into one location.

Test Plan

• Try out some different load syntaxes and make sure they raise errors, or don't raise them, according to your expectations.

Review requests

Is this a good idea to do now, or were we deliberately making people do mount="<something>"?

Risk assessment

Low.

[codecov]

Codecov Report

Merging #14187 (4f0845e) into chore_release-7.1.0 (165a607) will decrease coverage by 0.01%.
Report is 12 commits behind head on chore_release-7.1.0.
The diff coverage is n/a.

Additional details and impacted files

@@                   Coverage Diff                   @@
##           chore_release-7.1.0   #14187      +/-   ##
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- Coverage                70.45%   70.45%   -0.01%     
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  Files                     2512     2512              
  Lines                    71237    71232       -5     
  Branches                  8982     8982              
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- Hits                     50189    50184       -5     
  Misses                   18849    18849              
  Partials                  2199     2199              

Flag	Coverage Δ
g-code-testing	96.44% <ø> (ø)
notify-server	89.13% <ø> (ø)

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Files	Coverage Δ
api/src/opentrons/protocol_api/protocol_context.py	92.07% <ø> (-0.24%)	⬇️

[SyntaxColoring]

I'm not sure when this prefix thing was true, but it is not true now and it's weird, so I'm removing it from the docs.

[ecormany]

🚮

[ecormany]

From docs side, go ahead with this. The docstrings will carry along no problem. I'm doing a huge refactor of the Pipettes page (#14189), to the point it's not compatible with rebasing, so I'll incorporate those changes by copy-paste into that branch.

[ecormany]

🚮