[projmgr] Clean-up processed contexts by solution reloading

[grasci-arm]

Address #2286
Complementary to #2279

The problem could be reproduced via RPC by loading a solution without errors, then introducing yml syntax errors and reloading the solution.
ProjMgr member variables related to context processing must be cleaned-up when reloading a solution.

[github-actions]

Test Results

    3 files     21 suites   13m 10s ⏱️
  431 tests   431 ✅ 0 💤 0 ❌
1 293 runs  1 293 ✅ 0 💤 0 ❌

Results for commit 07ed81f.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.24%. Comparing base (1728064) to head (07ed81f).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2291   +/-   ##
=======================================
  Coverage   66.24%   66.24%           
=======================================
  Files         181      181           
  Lines       36343    36346    +3     
  Branches    22544    22544           
=======================================
+ Hits        24074    24077    +3     
  Misses       7678     7678           
  Partials     4591     4591           

Flag	Coverage Δ
projmgr-cov	80.29% <100.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
tools/projmgr/src/ProjMgr.cpp	80.26% <100.00%> (+0.07%)	⬆️

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