Clarify relationship between duplicatesStrategy and ResourceTransformers

[Goooler]

Refs #2026.

[Copilot]

Pull request overview

Clarifies how Gradle’s duplicatesStrategy interacts with Shadow’s resource transforming/relocating, documenting that duplicate handling happens in Gradle’s CopySpec layer before Shadow’s ResourceTransformer processing.

Changes:

• Expands the NOTE explaining precedence of duplicatesStrategy over transforming/relocating.
• Adds a concrete example showing how DuplicatesStrategy.EXCLUDE can prevent transformer-based merging.
• Documents the warning behavior emitted when a transformer matches a resource while duplicatesStrategy is EXCLUDE.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (2)

docs/configuration/merging/README.md:92

• The documented warning output omits the third line that Shadow actually logs (the "See … for more details" line). Including it (or noting the snippet is truncated) keeps the docs aligned with the real build output.

    'META-INF/services/foo' is matched by com.github.jengelman.gradle.plugins.shadow.transformers.ServiceFileTransformer but its DuplicatesStrategy is EXCLUDE — duplicates may be silently dropped before the transformer processes them.
    Set it to INCLUDE or WARN to ensure all duplicates are processed by the transformer.

docs/configuration/merging/README.md:61

• The NOTE explains that duplicatesStrategy runs before Shadow's transformers, but the phrase "duplicate filtering" is a bit inaccurate because most strategies (e.g., WARN/FAIL/INCLUDE) aren’t filtering duplicates; they’re handling them. Rewording avoids implying duplicatesStrategy always drops inputs.

Because `ShadowJar` is a subclass of Gradle's `AbstractCopyTask`, duplicate filtering configured via
`duplicatesStrategy` is performed at Gradle's `CopySpec` processing layer **before** entries are passed to Shadow's
internal [`ResourceTransformer`][ResourceTransformer] engine.