feat: Improve error message on failed custom op validation

[aborgna-q]

Prints the node and operation in the error message.

Before:

$ hugr validate test.hugr
Error validating HUGR: Type arguments of node did not match params declared by definition: Wrong number of type arguments: 1 vs expected 0 declared type parameters

After:

$ hugr validate test.hugr
Error validating HUGR: Error in signature of operation 'Not' in Node(27): Type arguments of node did not match params declared by definition: Wrong number of type arguments: 1 vs expected 0 declared type parameters

[codecov]

Codecov Report

Attention: Patch coverage is 22.22222% with 7 lines in your changes missing coverage. Please review.

Project coverage is 87.66%. Comparing base (67bb8a0) to head (47fa4b0).

Files	Patch %	Lines
hugr-core/src/ops/custom.rs	22.22%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1416      +/-   ##
==========================================
- Coverage   87.67%   87.66%   -0.02%     
==========================================
  Files         118      118              
  Lines       20424    20431       +7     
  Branches    18042    18049       +7     
==========================================
+ Hits        17906    17910       +4     
- Misses       1727     1729       +2     
- Partials      791      792       +1     

Flag	Coverage Δ
python	91.81% <ø> (ø)
rust	87.11% <22.22%> (-0.02%)	⬇️

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