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Match CPython's wording for unresolvable nonlocal declarations (#388)

* Match CPython's wording for unresolvable nonlocal declarations (#187)

visitNonLocalStmt fell back to the generic NameNotFoundError when a
nonlocal name has no binding in any enclosing function scope. CPython
raises a specific SyntaxError for this exact diagnostic:

    SyntaxError: no binding for nonlocal 'x' found

The generic fallback also produced a misleading "Perhaps you meant to
type 'x'?" suggestion in cases where a same-named binding exists in
scope but is unreachable (e.g. an intermediate function declares the
same name global, correctly blocking nonlocal from skipping past it) —
the Levenshtein-closest match is the identifier itself, since a name
reaching this point is by definition already spelled correctly.

Reuse ScopeConflictError (already used for the sibling #178-#181
nonlocal/global scope-conflict diagnostics, and whose reported error
name is literally "SyntaxError", matching CPython's own exception
class here) instead of introducing a new error class, and never call
suggestName for this case — there is nothing sensible to suggest.

Updated wasm-functions.spec.ts's "cannot declare parameter as
nonlocal" test: it was incidentally also asserting a NameNotFoundError
was present, since the same name failed both the #179 parameter/
nonlocal conflict and (as an unrelated side effect) the "no binding"
check; now asserts the more accurate ScopeConflictError.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017w4FqCep4j8XyFpF4kpVue

* Resolve nonlocal-error tests once instead of twice per assertion

Both tightened tests were calling toPythonAstAndResolve(code, 3) a
second time just to check for the absence of the "Perhaps you meant"
suggestion, re-parsing and re-resolving the same source for no
reason. Capture the thrown error once and assert both regexes
against its message instead.

Co-Authored-By: Claude Sonnet 5 ... (continued)

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