🐛 Fix TaggedValue Iterable masquerade

[elinscott]

Problem

TaggedValue (the wrapt.ObjectProxy node-graph wraps a socket's value in) always exposed __iter__, because wrapt.ObjectProxy forwards every dunder at the C level regardless of what it wraps. That made isinstance(TaggedValue(1.5), collections.abc.Iterable) report True for a wrapped scalar, even though actually calling iter(...) on it raised TypeError.

This PR closes the Iterable-masquerade itself, for every wrapped scalar; whether that alone makes a given wrapped value pass clean_value depends on what else that function checks.

In practice a wrapped float/int becomes storable, but a wrapped bool still returns the proxy (bool can't be subclassed, so isinstance(TaggedValue(True), bool) stays False) and a wrapped None still fails validation (value is None doesn't hold for the proxy) — both known residuals this PR does not resolve.

>>> from collections.abc import Iterable
>>> isinstance(TaggedValue(1.5), Iterable)
True          # before this fix
>>> iter(TaggedValue(1.5))
TypeError: ...

Changes

• TaggedValue.__new__ now dispatches on the wrapped value's actual iterability, returning a _TaggedScalar (which shadows __iter__ with None) for non-iterables and a _TaggedIterable (which inherits the proxy's forwarding __iter__) otherwise. Python's Iterable.__subclasshook__ treats __iter__ = None as "intentionally unset" and answers False.
• The dispatch is transparent to every other TaggedValue behaviour: arithmetic, equality, the socket= kwarg, copy/deepcopy, and serialization all still forward through the wrapped value exactly as before.

Testing

• Added TestTaggedValueIterable (tests/test_socket.py): a wrapped scalar (float, int, complex, None, bool) is not Iterable and raises TypeError on iter(), while still proxying arithmetic and equality; a wrapped list/tuple/dict/str/set is Iterable and iterates to the same elements as the unwrapped value; the socket= kwarg survives dispatch on both branches.
• Negative control (reproduced): reverting the __new__ dispatch while keeping the new tests fails 2 of them (test_scalar_is_not_iterable, test_socket_kwarg_preserved_on_scalar_and_iterable) — confirming the tests exercise the fix, not something already true beforehand.
• Full suite: 317 passed on this branch (upstream main's suite plus the new tests), no regressions.

[codecov]

Codecov Report

❌ Patch coverage is 97.29730% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.71%. Comparing base (8d85e61) to head (62c622d).

Files with missing lines	Patch %	Lines
src/node_graph/socket.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #177      +/-   ##
==========================================
+ Coverage   89.68%   89.71%   +0.03%     
==========================================
  Files          81       81              
  Lines        8984     9021      +37     
==========================================
+ Hits         8057     8093      +36     
- Misses        927      928       +1     

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