Fix invalid tick frequency in core library.

[Oberacda]

Related to #129

This PR should fix two issues:

• Invalid reporting of tick performance
• Non adherance to the specified tick frequency

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.

Project coverage is 49.62%. Comparing base (e2a5386) to head (dc22460).

Files with missing lines	Patch %	Lines
ros_bt_py/ros_bt_py/tree_manager.py	0.00%	14 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #130      +/-   ##
==========================================
+ Coverage   49.60%   49.62%   +0.01%     
==========================================
  Files          59       59              
  Lines        7678     7675       -3     
  Branches     1647     1647              
==========================================
  Hits         3809     3809              
+ Misses       3805     3802       -3     
  Partials       64       64              

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Test Results

  3 files  ±0    3 suites  ±0   41s ⏱️ -1s 181 tests ±0  181 ✅ ±0  0 💤 ±0  0 ❌ ±0  543 runs  ±0  543 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit dc224604. ± Comparison against base commit e2a53861.

:recycle: This comment has been updated with latest results.