feat: propagate step outputs across steps

[lukkaempf]

Explanation

Currently, outputs defined in a test step are only available within that same step.
This PR propagates outputs across steps, so a binding set via outputs in step N is
available in step N+1 and beyond. This is an addition of new behavior.

Related issue

Fixes #2464

Proposed Changes

runStep now returns the updated TestContext (including output bindings) in addition to the stop signal.
The step loop passes this context to subsequent steps, making outputs from one step available in the next.

Named return values are used so that catch/finally deferred blocks can also propagate their outputs —
without them, deferred changes to the context would be lost before the function returns.

Story Proces

1. Prior to this PR, outputs were scoped to a single step — a binding set via outputs
   in step N could not be referenced in step N+1.

2. This PR returns the updated TestContext from runStep and passes it to subsequent
   steps in the step loop.

3. After this PR, outputs from step N are available as bindings in all following steps.

Proof Manifest

apiVersion: chainsaw.kyverno.io/v1alpha1
kind: Test
metadata:
  name: step-outputs
spec:
  steps:
  - name: get-namespace-name
    try:
    - script:
        content: echo $NAMESPACE
        outputs:
        - name: ns
          value: (trim_space($stdout))
  - name: assert-namespace-exists
    try:
    - assert:
        resource:
          apiVersion: v1
          kind: Namespace
          metadata:
            name: ($ns)

Checklist

• I have read the contributing guidelines.
• I have read the PR documentation guide and followed the process including adding proof manifests to this PR.
• This is a bug fix and I have added unit tests that prove my fix is effective.

Further Comments