Improve Module 3 exercise

[xaru8145]

What this PR does

In module 3, avoid misleading constructor test failure when parameter declare and get have intentional typos to force the user to fix node parameter definitions.

3: [==========] Running 7 tests from 2 test suites.
3: [----------] Global test environment set-up.
3: [----------] 4 tests from TestLaserDetectorNodeConstructor
3: [ RUN      ] TestLaserDetectorNodeConstructor.CreatingANodeDoesNotThrow
3: /home/developer/ws/src/module_3/test/test_laser_detector_node.cpp:84: Failure
3: Expected: { const LaserDetectorNode dut(default_node_options_); } doesn't throw an exception.
3:   Actual: it throws rclcpp::exceptions::ParameterNotDeclaredException with description "footprint_radius".
3: 
3: [  FAILED  ] TestLaserDetectorNodeConstructor.CreatingANodeDoesNotThrow (30 ms)
3: [ RUN      ] TestLaserDetectorNodeConstructor.EvaluateConstructorDeclaresParameters
3: unknown file: Failure
3: C++ exception with description "footprint_radius" thrown in the test body.
3: 
3: [  FAILED  ] TestLaserDetectorNodeConstructor.EvaluateConstructorDeclaresParameters (17 ms)
3: [ RUN      ] TestLaserDetectorNodeConstructor.EvaluateConstructorReadsParameters
3: unknown file: Failure
3: C++ exception with description "footprint_radius" thrown in the test body.
3: 
3: [  FAILED  ] TestLaserDetectorNodeConstructor.EvaluateConstructorReadsParameters (17 ms)

To solve this, we define the typo in the same parameter for both declare and get functions, obtaining a meaningful error rather than an uncontrolled exception:

3: [ RUN      ] TestLaserDetectorNodeConstructor.EvaluateConstructorDeclaresParameters
3: [INFO] [1762367206.043342909] [laser_detector_node]: LaserDetectorNode initialized
3: /home/developer/ws/src/module_3/test/test_laser_detector_node.cpp:97: Failure
3: Value of: dut.has_parameter("min_points")
3:   Actual: false
3: Expected: true
3: 
3: [  FAILED  ] TestLaserDetectorNodeConstructor.EvaluateConstructorDeclaresParameters (15 ms)

Also, fix intentional typo in subscriber and place it on the publisher. The test covers the publisher and the test for the subscriber is on the user side. This is a more natural exercise flow.

Type

• Bugfix
• Feature
• Documentation

How to test

Steps to reproduce / test the changes:

1. Apply solutions to module 2.
2. Build module 3
3. Test module 3
4. Repeat steps 2 and 3 incrementally as you solve the bugs and complete the tests.

Checklist

• I have signed my commits (git commit -s) or added Signed-off-by to existing commits.
• I added/updated tests (if applicable)
• I updated documentation (if applicable)

Related issues

N/A

[JesusSilvaUtrera]

LGTM, just remeber to adapt the solutions branch acocrdingly, thanks!