(towards #2551) Add DUC positions caching

[sergisiso]

This is just a git checkout origin/2551_omp_barrier_Removal -- src/psyclone/psyir/tools/definition_use_chains.py, from @LonelyCat124 branch that I already reviewed but that branch still have some integration test issues to fix. However his change in this file brings the processing time of some NEMO files significantly down. And will be very convenient to already merge.

The most extreme case is:

to:

The time without profiling is 8s.
PS: these flamecharts are now fully-connected because we got rid of the eval in #3045 :)

[sergisiso]

@arporter @LonelyCat124 I suggest we already merge this change from #2967 as it speed-up all NEMO integration tests significantly. Ready for review

[sergisiso]

I added the caching also somewhere else because I saw that it also dominated the backend time, with this the result is:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.90%. Comparing base (dc66e55) to head (cbe7421).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3075   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files         367      367           
  Lines       51755    51758    +3     
=======================================
+ Hits        51705    51708    +3     
  Misses         50       50           

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