test: increase nebula_core_common unit coverage

[mojomex]

PR Type

• Improvement

Related Links

• Follow-up vendor-specific coverage PRs:
  • test: cover nebula_hesai_common helpers #427
  • test: cover nebula_robosense_common parser #428
  • test: cover nebula_velodyne_common calibration #429

Description

This PR increases coverage of nebula_core_common and adds focused unit tests for vendor-independent helpers.

Main additions:

• enum/string conversion coverage for ReturnType, ReturnMode, SensorModel, and Status
• stream-operator coverage for the core configuration structs and representative point-conversion helpers
• direct coverage for ring_buffer, bitfield, expected, rate_limiter, stopwatch, errno, and string conversion utilities
• unsigned edge-case coverage for get_bitfield() across uint8_t, uint16_t, and uint32_t

Small code fixes discovered while adding coverage:

• add missing Pandar128E3X handling in core sensor-model conversion helpers
• add the missing CAN_CONNECTION_ERROR branch in status streaming
• make bitfield explicitly require unsigned integral storage and simplify mask construction
• initialize the errno buffer to avoid the compiler warning treated as an error

Review Procedure

1. Review the PR commit-by-commit; the core coverage work is intentionally split into small commits.
2. In nebula_common tests, check that round-trip/default-case coverage reflects the public conversion helpers without overfitting stream formatting.
3. In the utility-helper tests, focus on the new unsigned-only bitfield contract and the added edge-case coverage for full-width extraction.
4. Sanity-check the small production fixes in nebula_common.hpp, nebula_status.hpp, bitfield.hpp, and errno.hpp that were exposed by the added tests.

Remarks

Verification used while preparing this PR:

• source /opt/ros/humble/setup.bash && colcon build --packages-select nebula_core_common --symlink-install --mixin debug compile-commands coverage-gcc
• source /opt/ros/humble/setup.bash && colcon test --packages-select nebula_core_common --event-handlers console_direct+

The repo-wide build-test-cov.sh run succeeds through coverage generation after splitting the vendor-specific work into follow-up PRs, but there is still an unrelated existing failure in nebula_core_hw_interfaces (TestTcp.TestConnectTimeout) that is not addressed here.

Pre-Review Checklist for the PR Author

PR Author should check the checkboxes below when creating the PR.

• Assign PR to reviewer

Checklist for the PR Reviewer

Reviewers should check the checkboxes below before approval.

• Commits are properly organized and messages are according to the guideline
• (Optional) Unit tests have been written for new behavior
• PR title describes the changes

Post-Review Checklist for the PR Author

PR Author should check the checkboxes below before merging.

• All open points are addressed and tracked via issues or tickets

CI Checks

• Build and test for PR: Required to pass before the merge.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.73%. Comparing base (ac59892) to head (21b942c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #425      +/-   ##
==========================================
+ Coverage   39.72%   48.73%   +9.01%     
==========================================
  Files         128      165      +37     
  Lines       10018    13365    +3347     
  Branches     4977     6962    +1985     
==========================================
+ Hits         3980     6514    +2534     
- Misses       5443     5476      +33     
- Partials      595     1375     +780     

Flag	Coverage Δ
nebula_core_common	87.46% <100.00%> (?)

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