Add API to count term size for a complex type

[lsrcz]

This pull request adds the API to count term size for complex types.

For example,

>>> allSymsSize ("a" :: SymInteger, "a" + "b" :: SymInteger, ("a" + "b") * "c" :: SymInteger)
5

Here the result is 5 as the same subterm will be counted for only once, and there are 5 distinct subterms:

• a
• b
• c
• (+ a b)
• (* (+ a b) c)

[codecov]

Codecov Report

Base: 32.99% // Head: 32.57% // Decreases project coverage by -0.42% ⚠️

Coverage data is based on head (e9c9b09) compared to base (a6de4ac).
Patch coverage: 5.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
- Coverage   32.99%   32.57%   -0.42%     
==========================================
  Files          47       47              
  Lines        4364     4423      +59     
  Branches      214      215       +1     
==========================================
+ Hits         1440     1441       +1     
- Misses       2710     2767      +57     
- Partials      214      215       +1     

Impacted Files	Coverage Δ
src/Grisette/Core/Control/Monad/UnionM.hs	9.71% <0.00%> (-0.06%)	⬇️
src/Grisette/Core/Data/Union.hs	45.16% <0.00%> (-1.00%)	⬇️
src/Grisette/IR/SymPrim/Data/SymPrim.hs	20.00% <0.00%> (-4.21%)	⬇️
...tte/IR/SymPrim/Data/Prim/InternedTerm/TermUtils.hs	37.02% <75.00%> (+0.34%)	⬆️
.../Grisette/IR/SymPrim/Data/Prim/PartialEval/Bool.hs	86.66% <0.00%> (-0.45%)	⬇️

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