docs(v2.0.0-alpha.3): inline plot injection across the entire doc tree

Add scripts/inject_doc_plots.py that scans every .md and .rst page under
docs/source/, executes each Python code-block in an isolated namespace
with a non-interactive matplotlib backend, captures every figure
produced, and inserts an inline image directive immediately after the
code-block.  Markers AUTO-PLOT-BEGIN/END make the injection idempotent
on re-runs.  Blocks that fail to execute or produce no figure are left
untouched.

Add a transparent __getattr__ fallback in python/optimizr/__init__.py
that forwards any unresolved top-level attribute to the compiled _core
extension.  This lets all v1.x and v2.0 doc samples that use
'from optimizr import X' (estimate_ou_params_py, linear_bsde_constant_coeffs,
mmd_gaussian, ...) execute as written.

Augment the OU Parameter Estimation example
(docs/source/algorithms/optimal_control.md) with a two-panel
visualization (simulated path plus empirical/theoretical autocorrelation).

Net effect: 14 doc pages now display matplotlib plots inline directly
under the code that produced them -- including the OU page, point
processes, Grid Search, HMM, MCMC, plus the 8 v2.0 RST pages.

python/optimizr/__init__.py

@@ -103,3 +103,20 @@ __all__ = [
     "min_variance_weights",
     "erc_weights",
 ]
+
+
+def __getattr__(name):
+    """Transparent fallback: forward any unresolved top-level attribute access
+    to the compiled `_core` extension.  This keeps `from optimizr import X`
+    working for every Rust-backed function (v1.x and v2.0 primitives) without
+    having to enumerate the full list above."""
+    try:
+        from optimizr import _core as _ext
+    except ImportError as exc:  # pragma: no cover
+        raise AttributeError(
+            f"module 'optimizr' has no attribute {name!r} "
+            f"(_core extension is not built: {exc})"
+        ) from exc
+    if hasattr(_ext, name):
+        return getattr(_ext, name)
+    raise AttributeError(f"module 'optimizr' has no attribute {name!r}")