Cleanup the API of dfcc_loop_nesting_grapht

[tautschnig]

Please review commit-by-commit.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.16 🎉

Comparison is base (535e6b2) 78.38% compared to head (fe428ad) 78.55%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7693      +/-   ##
===========================================
+ Coverage    78.38%   78.55%   +0.16%     
===========================================
  Files         1686     1686              
  Lines       192915   192915              
===========================================
+ Hits        151215   151539     +324     
+ Misses       41700    41376     -324     

Impacted Files	Coverage Δ
src/analyses/loop_analysis.h	100.00% <ø> (ø)
...nstrument/contracts/dynamic-frames/dfcc_cfg_info.h	100.00% <ø> (ø)
...trument/contracts/dynamic-frames/dfcc_cfg_info.cpp	78.63% <100.00%> (ø)
...ntracts/dynamic-frames/dfcc_loop_nesting_graph.cpp	96.66% <100.00%> (ø)

... and 21 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.