[commands] Lower SysId default step voltage

[TLNing260310]

Summary

• lower the default SysId dynamic step voltage from 7 V to 4 V in Java, C++, and Python
• make the Java, C++, and Python SysIdRoutine examples configure the step voltage explicitly and tell users to adjust it for their mechanism
• update the existing dynamic-voltage regression tests for the new default

Validation

• wpiformat 2026.71 (including C++ lint)
• Black formatting check for the changed Python files
• Python syntax compilation
• stale 7 V reference scan across the implementations, tests, and SysId examples

The focused compiled tests could not be started locally because this Windows environment has no JDK, and the repository-pinned Bazel binary download timed out. GitHub Actions will run the project build and test matrix.

Closes #7794

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-01T05:23:53.678176Z	7836dd2	PR opened

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[TLNing260310]

Documentation companion: wpilibsuite/wpilib-docs#3356