feat: hesai timezone unit tests

[mojomex]

PR Type

• Improvement

Related Links

#78 fix: hesai_decoder replace mktime with timegm -- the motivation for this PR
#80 Generic hesai unit tests -- unit test refactoring which this PR depends on

Description

Depends on #80 Generic hesai unit tests.

This PR implements a unit test for all Hesai sensor models which tests for correct timezone handling.
The expected decoder behavior is that, regardless of system timezone settings, pointcloud timestamps
are output in UST.
As demonstrated by #78, using the wrong function to parse timestamps can lead to timezone-dependent behavior,
which was, until now, hard to catch during development.

The new unit test sets the process' timezone settings to different values and decodes the same rosbag in each of them.
The pointcloud timestamps as returned by HesaiDriver::ConvertScanToPointcloud, decoded in different timezones, are then checked for equality.

Review Procedure

Change between mktime and gmtime in line 59 in hesai_packet.hpp, compile and run the unit tests.
They should fail for mktime and pass for timegm, as pointed out in #78.

With timegm:

1: [       OK ]

With mktime:

1: .../hesai_ros_decoder_test_main.cpp:137: Failure
1: Expected equality of these values:
1:   decoded_timestamps.back()
1:     Which is: 1504682387
1:   decoded_timestamps_cmp.back()
1:     Which is: 1504714787
...
1: [  FAILED  ]

The timestamps can be converted to human-readable form in the terminal using date -ud @<timestamp>:

$ date -ud @1504682387
2017年  9月  6日 水曜日 07:19:47 UTC
$ date -ud @1504714787
2017年  9月  6日 水曜日 16:19:47 UTC

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Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (6ceea8d) 8.03% compared to head (e6ac003) 31.80%.

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Additional details and impacted files

@@            Coverage Diff             @@
##            main      #81       +/-   ##
==========================================
+ Coverage   8.03%   31.80%   +23.76%     
==========================================
  Files        108        7      -101     
  Lines       9069      742     -8327     
  Branches     844      463      -381     
==========================================
- Hits         729      236      -493     
+ Misses      7778       94     -7684     
+ Partials     562      412      -150     

Flag	Coverage Δ
differential	31.80% <25.00%> (?)
total	?

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Files	Coverage Δ
nebula_tests/hesai/hesai_ros_decoder_test_main.cpp	31.25% <25.00%> (-2.85%)	⬇️

... and 101 files with indirect coverage changes

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[amc-nu]

@mojomex We tested this branch, and it works correctly. Thank you.
Could you please resolve the conflicts raised with #80

[mojomex]

@amc-nu All resolved, thank you for reviewing!