fix(executor): name the exact field when a Function block reference holds a large value - #8474

Summary

• When a Function block reference holds a large value below its root (e.g. contents: [<large value>]), the error now names the exact field to reference instead of the generic "This execution value contains nested large values": <file.contents> contains a 10.5 MB value at <file.contents[0]>. Reference that field directly.
• Runtimes that cannot load a large value on demand (Python, shell, JavaScript with imports) get Select a smaller field, or read it in JavaScript without imports. instead of being pointed at a reference that would fail the same way
• A reference pointing straight at a large value in those runtimes now names the reference and its size, and a large array no longer gets the misleading "nested" message
• Keys that can't be written as a reference (dots, spaces, operators) omit the field path rather than suggesting an invalid one; array manifests are named as the field rather than their internal chunks
• Throw behavior is unchanged — only the message. The walk stops at the first large value like containsLargeValueRef, reads the size already stored on the ref, loads nothing, and only runs when we're about to throw

Type of Change

• Bug fix

Testing

• executor/variables suite (129 tests); 7 new/changed assertions, all red against the previous resolver
• Removed each new guard (key escaping, runtime remedy, stop at manifests) and watched its test go red
• bun run type-check, bun run lint, bun run check:audits (52/52), docs-manifest:check

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)