feat: deprecate in favor of webpack's output.copy

[alexander-akait]

Summary

webpack copies files itself since 5.111.0 (webpack/webpack#21938), through output.copy and the webpack.CopyPlugin behind it, so this package is no longer needed there. Adds a one-time DeprecationWarning and a README section saying what each option becomes, linking the worked example in webpack's examples/output-copy.

The warning is a capability check, not a version comparison: it fires only when the compiler's compiler.webpack has CopyPlugin, so anyone on an older webpack — where this plugin is still the answer — sees nothing.

What kind of change does this PR introduce?

feat

Did you add tests for your changes?

Yes — test/deprecation.test.js covers the warning's message, type and code, that it fires once across several compilers, and that it stays silent both when webpack cannot copy files itself and when there is no compiler.webpack at all.

Does this PR introduce a breaking change?

No. The package keeps working unchanged; only a Node deprecation warning is added, which --no-deprecation silences like any other.

If relevant, what needs to be documented once your changes are merged or what have you already documented?

The README carries the deprecation notice, the migration diff and the option-by-option table. If the package is later marked deprecated on npm, the same text fits.

Use of AI

Claude Code wrote the deprecation warning, the tests and the README section, and verified them: lint:prettier, lint:code, lint:spelling and lint:types all pass, and the full suite is green (15 suites, 264 tests). It also checked the migration table against both option schemas rather than from memory, and corrected one claim it had got wrong — a late processAssets stage does not keep a copied file out of the minimizer, because the minimizer taps with additionalAssets: true and so re-runs for assets added later; info: { minimized: true } is what does.

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Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.21%. Comparing base (08b3a64) to head (9ab3543).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #839      +/-   ##
==========================================
+ Coverage   92.00%   92.21%   +0.20%     
==========================================
  Files           2        2              
  Lines         413      424      +11     
  Branches      124      126       +2     
==========================================
+ Hits          380      391      +11     
  Misses         32       32              
  Partials        1        1              

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