fix(stdlib): pop also removes last item from type definition

[JakubOnderka]

Summary

Before

$ int(pop([1,2,3])[2])
function call error for "int" at (0:20): expected integer, got null

After

$ int(pop([1,2,3])[2])

error[E100]: unhandled error
  ┌─ :1:1
  │
1 │ int(pop([1,2,3])[2])
  │ ^^^^^^^^^^^^^^^^^^^^
  │ │
  │ expression can result in runtime error
  │ handle the error case to ensure runtime success
  │
  = see documentation about error handling at https://errors.vrl.dev/#handling
  = learn more about error code 100 at https://errors.vrl.dev/100
  = see language documentation at https://vrl.dev
  = try your code in the VRL REPL, learn more at https://vrl.dev/examples

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

cargo test

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on
  our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

• Our CONTRIBUTING.md is a good starting place.
• If this PR introduces changes to LICENSE-3rdparty.csv, please
  run dd-rust-license-tool write and commit the changes. More details here.

[chatgpt-codex-connector]

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[pront]

@JakubOnderka codex called out this example. Related to arrays with different lengths.