refactor: Better error message on allocation failure.

[ss2165]

Wait to merge for hugr 0.15.3 release including CQCL/hugr#2032

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.46%. Comparing base (03627a7) to head (e57bc22).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
tket2-hseries/src/extension/qsystem.rs	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #827   +/-   ##
=======================================
  Coverage   82.46%   82.46%           
=======================================
  Files          66       66           
  Lines        8274     8276    +2     
  Branches     8005     8007    +2     
=======================================
+ Hits         6823     6825    +2     
  Misses       1044     1044           
  Partials      407      407           

Flag	Coverage Δ
python	81.78% <ø> (ø)
rust	82.49% <66.66%> (+<0.01%)	⬆️

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