ENH: Add Support for dict unpacking in csp.node

[aadya940]

Reference Issue:

Closes #725

Dict Unpacking via ** now works as shown above instead of a CspParseError.

This includes the following:

Single dict Unpacking:

 **{"a1": 1, "a2": 2}

Nested dicts:

**{"a1": 1, "a2": {"a1": 1, "a2": 2}}

Multiple dicts

 (**d1, **d2)

How

Named outputs get resolved at parse time: csp.output(a=1) rewrites to #outp_0 + 1. That can't work for **values, since the keys only exist once the node ticks.

So the parser detects the unpack (ast.keyword with arg=None) and emits a call to a small runtime helper, passing a statically-built {name: proxy} map alongside the unpacked expression. The helper iterates the dict at runtime and ticks each output via the same proxy + value mechanism the generated code already uses. No C++ changes needed, since PyOutputProxy already exposes this through nb_add.

[AdamGlustein]

Thanks for the contribution, this is great! Just some minor comments to address.

[AdamGlustein]

Please add a comment here noting we override the ast.Add operator to output a value, elsewise this code looks like it's dead. You may also need to do a ruff noqa to tell ruff to ignore it

[AdamGlustein]

Nit: you can remove _CSP_OUTPUT_KWARGS_FUNC from the dicts here and just call _csp_output_kwargs in the ast.Call node directly. These dictionaries are meant for functions defined in the C++ code.

[robambalu]

we can try to avoid the function call overhead and generator the for loop AST directly here instead
note you can use @node( debug_print=True ) to dump the generated readable code for debugging

[aadya940]

Yes, I'm working on it, I saw the dict creation per tick is actually more expensive than the jump to the function call, so hopefully minimizing that too, so the same dict can be reused with different runtime values.