fix(types): isolate test ownership state and type string cloning

Problem

The examples acceptance gate has two ownership-related failures:

1. ItTestDecl bodies are checked in the preceding function's drop state. A string local named result is dropped at the end of one test; a later it(...) test reuses result for an integer, does not register a drop, and is falsely diagnosed as using the earlier dropped variable.
2. ownership_test.home assigns one owned string directly to another binding and then uses both, even though Home's ownership tests define strings as move-only. The example comment claims both that strings move and that this use should work.

Scope

• Add an ownership flow-state reset that preserves accumulated diagnostics and registered behavior.
• Give function and it test bodies isolated ownership/drop/type environments and balanced scopes.
• Recognize string.clone() / string.copy() as returning a string.
• Update the ownership example to clone explicitly instead of weakening string move semantics.
• Add focused checker regressions and re-run examples.

Acceptance criteria

• Reusing a local name across adjacent test declarations cannot inherit dropped/moved state.
• String clone/copy calls preserve their receiver for later use.
• Direct string assignment remains a move.
• ownership_test.home and strings.test.hm pass home check.

Part of #779 and #814.

Completed by a5faf23a2 on origin/main. Ownership facts now reset between callable/test bodies with balanced scopes, it declarations use isolated type/drop environments, and string clone/copy retain string result types. The ownership example now clones explicitly, preserving the established move-only string rule. Guarded verification: checker 74/74, no-JSC build 2,841 MB, examples 38 pass / 1 fail; both ownership_test.home and strings.test.hm now pass.