Document PHPStan meta() return-type extension usage

[Copilot]

The README template did not explain how consumers can enable PHPStan support for YourArrayySubclass::meta(). This left the custom return-type extension discoverable in the codebase, but not in the published docs.

• What changed

  • Added a focused section to the PHPDoc array-shape / property-checking docs in build/docs/base.md.
  • Regenerated README.md so the published documentation includes the same guidance.

• PHPStan integration

  • Documents when the extension is useful: projects that use meta() with PHPStan and want literal-string/object-shape inference for meta keys.
  • Explains the practical effect: expressions like $userMeta->id resolve to 'id', nested meta-key access stays typed, and invalid properties such as $userMeta->ghost can be reported.

• Consumer setup

  • Adds the PHPStan service registration snippet needed to enable Arrayy\PHPStan\MetaDynamicStaticMethodReturnTypeExtension.
  • Clarifies that the repository’s own phpstan.neon is not shipped with the Composer package, so users should copy the service definition into their project config.

services:
    -
        class: Arrayy\PHPStan\MetaDynamicStaticMethodReturnTypeExtension
        tags:
            - phpstan.broker.dynamicStaticMethodReturnTypeExtension

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This change is 

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[coveralls]

coverage: 92.079% (-0.3%) from 92.38% — copilot/update-readme-custom-phpstan-extension into master