feat: add methods to Subcircuit for finding const inputs

[acl-cqc]

Final part of Luca's #1273, following #1288 and #1289.

I've broken these bits out because I think we should probably be doing much less here and should rely on Constant Folding to remove the conversions etc.

[codecov]

Codecov Report

❌ Patch coverage is 73.34852% with 234 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.67%. Comparing base (0f1d700) to head (d53f8d5).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
tket/src/subcircuit.rs	74.78%	165 Missing and 14 partials ⚠️
tket/src/resource.rs	69.35%	18 Missing and 1 partial ⚠️
tket/src/rewrite/strategy.rs	5.00%	19 Missing ⚠️
tket/src/resource/scope.rs	85.71%	5 Missing and 2 partials ⚠️
tket/src/portmatching/matcher.rs	33.33%	4 Missing ⚠️
tket/src/resource/types.rs	0.00%	2 Missing ⚠️
tket/src/rewrite.rs	83.33%	1 Missing and 1 partial ⚠️
tket/src/rewrite/trace.rs	0.00%	1 Missing ⚠️
tket/src/subcircuit/interval.rs	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1290      +/-   ##
==========================================
- Coverage   79.46%   78.67%   -0.79%     
==========================================
  Files         160      161       +1     
  Lines       20378    21364     +986     
  Branches    19446    20398     +952     
==========================================
+ Hits        16194    16809     +615     
- Misses       3201     3560     +359     
- Partials      983      995      +12     

Flag	Coverage Δ
python	92.92% <ø> (+0.27%)	⬆️
qis-compiler	100.00% <ø> (ø)
rust	77.98% <73.34%> (-0.84%)	⬇️

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[hugrbot]

This PR contains breaking changes to the public Rust API.
Please deprecate the old API instead (if possible), or mark the PR with a ! to indicate a breaking change.

cargo-semver-checks summary

    Building tket v0.16.0 (current)
     Built [  44.423s] (current)
   Parsing tket v0.16.0 (current)
    Parsed [   0.102s] (current)
  Building tket v0.16.0 (baseline)
     Built [  42.852s] (baseline)
   Parsing tket v0.16.0 (baseline)
    Parsed [   0.092s] (baseline)
  Checking tket v0.16.0 -> v0.16.0 (assume minor change)
   Checked [   0.082s] 159 checks: 156 pass, 3 fail, 0 warn, 41 skip

--- failure auto_trait_impl_removed: auto trait no longer implemented ---

Description:
A public type has stopped implementing one or more auto traits. This can break downstream code that depends on the traits being implemented.
      ref: https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.45.0/src/lints/auto_trait_impl_removed.ron

Failed in:
type ModifierResolver is no longer Sync, in /home/runner/work/tket2/tket2/PR_BRANCH/tket/src/modifier/modifier_resolver.rs:303
type ModifierResolver is no longer UnwindSafe, in /home/runner/work/tket2/tket2/PR_BRANCH/tket/src/modifier/modifier_resolver.rs:303
type ModifierResolver is no longer RefUnwindSafe, in /home/runner/work/tket2/tket2/PR_BRANCH/tket/src/modifier/modifier_resolver.rs:303

--- failure function_missing: pub fn removed or renamed ---

Description:
A publicly-visible function cannot be imported by its prior path. A `pub use` may have been removed, or the function itself may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.45.0/src/lints/function_missing.ron

Failed in:
function tket::modifier::qubit_types_utils::contain_qubits, previously in file /home/runner/work/tket2/tket2/BASELINE_BRANCH/tket/src/modifier/qubit_types_utils.rs:14
function tket::modifier::qubit_types_utils::contain_qubit_term, previously in file /home/runner/work/tket2/tket2/BASELINE_BRANCH/tket/src/modifier/qubit_types_utils.rs:54

--- failure module_missing: pub module removed or renamed ---

Description:
A publicly-visible module cannot be imported by its prior path. A `pub use` may have been removed, or the module may have been renamed, removed, or made non-public.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.45.0/src/lints/module_missing.ron

Failed in:
mod tket::modifier::qubit_types_utils, previously in file /home/runner/work/tket2/tket2/BASELINE_BRANCH/tket/src/modifier/qubit_types_utils.rs:1

   Summary semver requires new major version: 3 major and 0 minor checks failed
  Finished [  89.764s] tket
  Building tket-qsystem v0.22.0 (current)
     Built [  44.704s] (current)
   Parsing tket-qsystem v0.22.0 (current)
    Parsed [   0.028s] (current)
  Building tket-qsystem v0.22.0 (baseline)
     Built [  44.556s] (baseline)
   Parsing tket-qsystem v0.22.0 (baseline)
    Parsed [   0.028s] (baseline)
  Checking tket-qsystem v0.22.0 -> v0.22.0 (assume minor change)
   Checked [   0.048s] 159 checks: 159 pass, 41 skip
   Summary no semver update required
  Finished [  91.152s] tket-qsystem