Support multiple top-level class wrappers in Playground BeanShell runner

[liannacasper]

Motivation

• Allow the Playground BeanShell runtime to accept scripts that declare multiple consecutive top-level classes and unwrap them into the script namespace rather than only a single top-level class.

Description

• Extend unwrapSingleTopLevelClass to accumulate and unwrap consecutive top-level class bodies instead of rejecting when more than one top-level class exists.
• Preserve existing safety checks by rejecting scripts with nested type declarations, non-whitespace code between class wrappers, or unsupported constructs, and continue to transformFieldDeclarations where needed.
• Add smokeMultipleClassWrapperScript() to PlaygroundSmokeHarness and call it from main() to exercise a two-class script (Helpers + Demo).
• Update the scripts/cn1playground/README.md text to reflect that top-level classes (plural) are unwrapped.

Testing

• Attempted to run the playground smoke harness via ./tools/run-playground-smoke-tests.sh which failed due to environment constraints (missing Java 8 toolchain and local CN1 build client artifacts), so the script could not complete in this environment.
• Ran mvn -pl common -am -DskipTests compile which reached the cn1playground-common build but failed during the CN1 bootstrap/download step because the environment could not fetch UpdateCodenameOne.jar (Network is unreachable) and a local cn1playground-ZipSupport artifact was missing.
• No functional test failures were observed in the edited source files themselves; the remaining failures are environmental and unrelated to the implemented logic changes.

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Codex Task

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