fix: small quirks surfaced while writing the test suite

[shbatm]

Three independent issues observed while building out the offline pytest suite (#484), grouped here because each is one or two lines and none warrants its own ticket.

1. Nodes.parse() re-update path silently dropped

pyisy/nodes/__init__.py line 415 (pre-fix) called the async Node.update(xmldoc=feature) from a synchronous parsing loop without await. The returned coroutine was never run, so when parse() re-encountered an existing address (the re-update branch) the node's status was never refreshed from the new XML. The test suite caught this as RuntimeWarning: coroutine 'Node.update' was never awaited.

Fix inlines the synchronous portion of Node.update(xmldoc=...) directly in the parser: capture last_update, merge aux_properties, and call update_state(state). No new public method on Node; the async Node.update is unchanged for its other callers.

2. NodeIterator missing __iter__

NodeIterator implemented __next__ and __len__ but not __iter__. Python's for protocol calls iter() on the iterable, which requires __iter__ on the iterator object itself — without it, for x in iter(nodes) and for x in reversed(nodes) raise TypeError. Added the conventional __iter__ returning self.

Programs reuses the same iterator class (aliased as ProgramIterator), so this fix covers both managers.

3. Programs.__getitem__ raised KeyError on unrecognized keys

The inner try around fun(val) returns None on KeyError/IndexError/ValueError, and the signature is -> Program | Folder | None — but the path where val isn't an address, isn't a known name, and can't be int()-converted raised KeyError("Unrecognized Key: ...") instead of returning None. Inconsistent with the other miss paths.

Fix returns None from that branch too, matching the rest of the method.

Test plan

Regression coverage lands in PR #484 (the test-suite PR), which already has the failing-warning case for #1 and tightens the Programs miss assertions for #3. No new tests in this PR — the fixes are small enough to review on their own.

HA Core impact

None. homeassistant/components/isy994/ doesn't iterate NodeIterator directly, doesn't call Programs.__getitem__("missing-key") with the expectation of a KeyError, and the dropped re-parse manifested as a stale cache the existing event-stream handlers immediately re-corrected.