add multi stream HX

[EvenSol]

The current implementation needs more work, but solves the case where a dominating hot feed stream is coold be two or more streams. See test;
src/test/java/neqsim/process/equipment/heatexchanger/MultiStreamHeatExchangerTest.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 45.66929% with 138 lines in your changes missing coverage. Please review.

Project coverage is 40.98%. Comparing base (c78f834) to head (36bfcb5).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ipment/heatexchanger/MultiStreamHeatExchanger.java	45.66%	131 Missing and 7 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1230      +/-   ##
============================================
+ Coverage     40.96%   40.98%   +0.01%     
- Complexity     5970     5988      +18     
============================================
  Files           718      719       +1     
  Lines         68019    68273     +254     
  Branches       8133     8163      +30     
============================================
+ Hits          27867    27983     +116     
- Misses        38473    38604     +131     
- Partials       1679     1686       +7     

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