Handle empty input gracefully

[mozesl-nokia]

Previously, running a ResourceListProcessor with the SDK and giving it a 0 length input resulted in a parsing error since we expected a KubeObject to be parsed from said input. This is now handled in this PR.

Added some extra unit tests for things I ran unto during debugging.

[Copilot]

Pull request overview

This PR updates the Go KRM Functions SDK to treat zero-length (or whitespace-only) input as an empty ResourceList, avoiding a parsing failure and adding regression tests around empty input/serialization.

Changes:

• Update ParseResourceList to return an empty ResourceList for empty/whitespace input.
• Harden empty ResourceList YAML serialization by avoiding nil dereferences around FunctionConfig.
• Add unit tests for Run([]byte{}), ParseResourceList([]byte{}), and ToYAML() on an empty ResourceList.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
go/fn/run_test.go	Adds a regression test asserting Run succeeds with empty input and returns a minimal ResourceList YAML.
go/fn/resourcelist.go	Treats empty input as an empty ResourceList; updates parse error message; avoids nil deref when serializing functionConfig.
go/fn/resourcelist_test.go	Adds tests for parsing zero bytes and serializing an empty ResourceList without panicking.
go/fn/object.go	Makes KubeObject.IsEmpty() safe to call on a nil receiver / nil internal object.

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