feat: _as_dict=True mode for high-performance figure construction

[AlonSpivack]

• I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the code generator and not the generated files.
• I have added tests or modified existing tests.
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Description

Adds _as_dict=True parameter to trace constructors and go.Figure for faster figure construction when validation is not needed.

When _as_dict=True:

1. Trace constructors return plain dicts with auto-injected type — no validation, no object creation
2. Figure constructor stores data/layout as raw lists/dicts — no deepcopy, no validators
3. Methods (add_traces, update_layout, add_vline, etc.) have fast paths that directly modify internal structures

Limitations

• add_vline/add_hline assume single-plot figures (row/col ignored)
• No validation — invalid properties pass through silently

Benchmarks

Operation	Speedup
Trace creation	~26x
Figure creation	~52x
Add traces	~36x
Add vline	~90,000x

Closes #5514

[AlonSpivack]

Implementation for #5514.
Discussion about the API naming (_as_dict vs as_dict)
is happening on the issue.