hal: Add C++ API (hal.hh) and pybind11 bindings on the new HAL API

Reintroduce a C++ interface after the getter/setter transition, built
strictly on the public C API and the user-land query API:

- hal.hh: type-safe C++ layer. Typed pin/param handles via traits<T>
  (compile-time accessor selection), runtime-typed pin_t variant and
  anypin (stored-type-tag multiplexing for name-based access), port
  wrapper, component class, and ULAPI by-name query/set functions.
  No hal_priv.h, no direct shared memory access, no re-implemented
  library internals.

  Handles re-read the shmem slot on every access so hal_link() slot
  rewrites stay visible (C pointer-variable semantics). Query callback
  exceptions are captured and re-thrown after the library releases the
  HAL mutex, so a throwing setter cannot wedge the session.

- halpybind.cc: pybind11 module (halpp.so) exposing component, Pin,
  hal_dir/hal_type_t enums and the by-name functions. Built alongside
  the existing _hal/hal.py, replacing nothing.

- tests/halpp: Python and native C++ smoke suites covering component
  lifecycle, typed pins/params, signals, linking, by-name get/set with
  type coercion and range checks, port pins and error paths.

Based on the pybind11 branch by rene-dev, re-based on the new HAL API.

Author: grandixximo

debian/control.top.in

@@ -40,6 +40,7 @@ Build-Depends:
     psmisc,
     python3,
     python3-dev,
+    python3-pybind11,
     python3-tk,
     python3-xlib,
     tcl,

src/hal/Submakefile

@@ -36,6 +36,19 @@ $(HALQUERY): $(call TOOBJS, $(HALQUERYSRCS)) $(HALLIB)
 	$(ECHO) Linking python module $(notdir $@)
 	$(Q)$(CC) $(LDFLAGS) -shared -o $@ $^
 
+# pybind11 C++ bindings (hal.hh based)
+HALPPSRCS := hal/halpybind.cc
+PYSRCS += $(HALPPSRCS)
+
+# pybind11 headers: python3-pybind11 (system include) or pip user site
+$(call TOOBJS, $(HALPPSRCS)): EXTRAFLAGS += $(shell python3 -m pybind11 --includes 2>/dev/null)
+
+HALPP := ../lib/python/halpp.so
+$(HALPP): $(call TOOBJS, $(HALPPSRCS)) $(HALLIB)
+	$(ECHO) Linking python module $(notdir $@)
+	$(Q)$(CXX) $(LDFLAGS) -shared -o $@ $^
+
 TARGETS += $(HALLIB) ../lib/liblinuxcnchal.so.0
 PYTARGETS += $(HALMODULE)
 PYTARGETS += $(HALQUERY)
+PYTARGETS += $(HALPP)