Add configure() overload to set the initial LPF state (backport #657)

[mergify]

Description

LowPassFilter always initializes its state from the first update() input, so there's
no way to start it from a known value.

This PR adds a configure(const T & initial_state) overload that seeds the state: the first
update() returns initial_state and the filter converges towards the input from there.

Fixes #643

Is this user-facing behavior change?

Yes, additive only. Existing configure() calls behave exactly as before.

Did you use Generative AI?

Implementation written by hand. Claude Code (Opus 5) reviewed it and helped write the unit tests.

Additional Information

The new tests cover all three supported types (double, std::vector<double>,
WrenchStamped). These are the first direct unit tests of control_toolbox::LowPassFilter;
the existing ones only reach it through the plugin.

TODOs

To send us a pull request, please:

• Fork the repository.
• Modify the source; please focus on the specific change you are contributing. If you also reformat all the code, it will be hard for us to focus on your change.
• Ensure local tests pass. (colcon test and pre-commit run (requires you to install pre-commit by pip3 install pre-commit)
• Commit to your fork using clear commit messages.
• Send a pull request, answering any default questions in the pull request interface.
• Pay attention to any automated CI failures reported in the pull request, and stay involved in the conversation.

---

This is an automatic backport of pull request #657 done by [Mergify](https://mergify.com).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.16%. Comparing base (dcb8ce9) to head (c73a28c).

Files with missing lines	Patch %	Lines
...oolbox/include/control_toolbox/low_pass_filter.hpp	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           kilted     #662      +/-   ##
==========================================
+ Coverage   82.78%   83.16%   +0.37%     
==========================================
  Files          29       30       +1     
  Lines        2004     2043      +39     
  Branches      113      115       +2     
==========================================
+ Hits         1659     1699      +40     
+ Misses        276      274       -2     
- Partials       69       70       +1     

Flag	Coverage Δ
unittests	83.16% <96.87%> (+0.37%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
control_toolbox/test/low_pass_filter_tests.cpp	100.00% <100.00%> (ø)
...oolbox/include/control_toolbox/low_pass_filter.hpp	88.46% <88.88%> (+0.22%)	⬆️

... and 1 file with indirect coverage changes

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