docs: add qsystem gate definitions

[CalMacCQ]

Testing out adding some gate definitions and doctests to the qsystem docs

Couple things

• potentially quite a pain to add defintions for all gates across std.qsystem and std.quantum.
• We would also have to duplciate content across qsystem and qsystem_functional (also quantum and qauntum_functional)
• Need to ensure the doctests are working properly

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.18%. Comparing base (d39b51c) to head (311af2c).

Additional details and impacted files

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##             main     #912   +/-   ##
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  Coverage   93.18%   93.18%           
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  Files          84       84           
  Lines        9628     9628           
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  Hits         8972     8972           
  Misses        656      656           

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[qartik]

It's worth noting that this version of measure is blocking unlike quantum.measure that is lazy. I am unsure if that should be documented here or now.

[qartik]

Never mind, I am wrong. Both of the variants of measure are lazy.

[ss2165]

1. Increasingly it looks like it would be handy to have a utility that defines and compiles a single function. To be used in exmamples, doc tests, prototyping, etc. @mark-koch are you opposed to adding a dedicated decorator for this? (prompted by having to call compile() at the end of the doctest)
2. Don't duplicate docs, cross-link to the non-functional one in each case. e.g. "Functional variant of zz_phase, see guppylang.std.qsystem.zz_phase"

[mark-koch]

are you opposed to adding a dedicated decorator for this?

If we use this in all examples then that's what people will copy and use themselves. So I think we have to be careful that this doesn't become an anti-pattern. In particular, it would be bad if people slapped that decorator on every function.

Also, where would you get the compiled Hugr from? Returning it from the decorator would make it hard to use those functions for comptime

[ss2165]

we have to be careful that this doesn't become an anti-pattern

yes good point, what about a kwarg to @guppy that makes it clear that this is a thing you shouldn't do normally? Or a check kwarg that only does the checking stage and not compilation to hugr?