[docs concepts/regular-expressions] replace "routine" with "method"

[chengjilai]

1. The term "routine" is potentially ambiguous in documentation.
2. The opening sentence already refers to them as "16 methods of Regexp", so this change ensures terminology consistency throught out the introduction.
3. This improves readability for new developers.

[github-actions]

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[Copilot]

Pull request overview

Updates the parsing-log-files concept introduction to use consistent Go regexp terminology by replacing the ambiguous word “routine” with “method”, aligning with the existing “methods of Regexp” phrasing.

Changes:

• Replace “routine” with “method” in the Regexp methods explanation.
• Normalize minor Markdown whitespace/trailing spaces in the edited sections.

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