feat!: ReplaceTypes: allow lowering ops into a Call to a function already in the Hugr

[acl-cqc]

There are two issues:

• Errors. The previous NodeTemplates still always work, but the Call one can fail if the Hugr doesn't contain the target function node. ATM there is no channel for reporting that error so I've had to panic. Otherwise it's an even-more-breaking change to add an error type to NodeTemplate::add() and NodeTemplate::add_hugr(). Should we? (I note HugrMut::connect panics if the node isn't there, but could make the NodeTemplate::add builder method return a BuildError...and propagate that everywhere of course)
• There's a big limitation in linearize_array that it'll break if the element says it should be copied/discarded via a NodeTemplate::Call, as linearize_array puts the elementwise copy/discard function into a nested Hugr (Value::Function) that won't contain the function. This could be fixed via lifting those to toplevel FuncDefns with name-mangling, but I'd rather leave that for Reduce duplication when linearizing arrays #2086 ....

BREAKING CHANGE: Add new variant NodeTemplate::Call; LinearizeError no longer derives Eq.

[codecov]

Codecov Report

Attention: Patch coverage is 93.93939% with 12 lines in your changes missing coverage. Please review.

Project coverage is 83.30%. Comparing base (89c2680) to head (5b29b4c).
Report is 1 commits behind head on release-rs-v0.16.0.

Files with missing lines	Patch %	Lines
hugr-passes/src/replace_types.rs	92.53%	5 Missing and 5 partials ⚠️
hugr-passes/src/replace_types/handlers.rs	50.00%	0 Missing and 1 partial ⚠️
hugr-passes/src/replace_types/linearize.rs	98.38%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                  Coverage Diff                   @@
##           release-rs-v0.16.0    #2094      +/-   ##
======================================================
+ Coverage               83.29%   83.30%   +0.01%     
======================================================
  Files                     219      218       -1     
  Lines                   42051    42102      +51     
  Branches                38153    38307     +154     
======================================================
+ Hits                    35026    35073      +47     
+ Misses                   5220     5218       -2     
- Partials                 1805     1811       +6     

Flag	Coverage Δ
python	85.42% <ø> (-0.31%)	⬇️
rust	83.09% <93.93%> (+0.04%)	⬆️

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[hugrbot]

This PR contains breaking changes to the public Rust API.

cargo-semver-checks summary

--- failure derive_trait_impl_removed: built-in derived trait no longer implemented ---

Description:
A public type has stopped deriving one or more traits. This can break downstream code that depends on those types implementing those traits.
      ref: https://doc.rust-lang.org/reference/attributes/derive.html#derive
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.41.0/src/lints/derive_trait_impl_removed.ron

Failed in:
type LinearizeError no longer derives Eq, in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-passes/src/replace_types/linearize.rs:140

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.41.0/src/lints/enum_variant_added.ron

Failed in:
variant NodeTemplate:Call in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-passes/src/replace_types.rs:51

[ss2165]

1. I think if you're breaking anyway might as well break with a proper error too (i.e. since it will have to go in a breaking release, fixing downstream is low cost)
2. annoying edge case - document and panic on detection if possible

[acl-cqc]

Ok, so NodeTemplate::add_hugr already returned an error, but NodeTemplate::add needed one. And, the errors from both needed to be plumbed through ReplaceTypesError and LinearizeError.

I started trying to add my own error for add_hugr (see 5daa87b), but then realized that since I needed to plumb BuildErrors through from add I switched to just use that. The alternative would be to look for all the error cases myself (as in that linked commit, but before calling the builder) and then unwrap the builder call....nicer for our users perhaps but seems less maintainable. And I think it's a small point. But I could be arm-twisted...

[ss2165]

happy to see many unwraps go away

[ss2165]

Suggested change

	/// A Call to a function (already) existing in the Hugr.
	/// A Call to an existing function.