Register Python dbg object as magic variable in debugger scripting console

[Copilot]

This PR implements automatic registration of the dbg magic variable in the Python scripting console, allowing users to access the debugger controller directly without manual instantiation.

Background

Previously, users had to manually create a DebuggerController instance in the Python console:

# Before this change
dbg = DebuggerController(bv)
dbg.launch_and_wait()

Changes

Following the pattern established in the BinaryNinja API (scriptingprovider.py lines 1532-1535) and the kernelcache plugin, this PR adds:

1. _get_debugger function: Creates a DebuggerController instance for the currently active binary view
2. Magic variable registration: Registers "dbg" using binaryninja.PythonScriptingProvider.register_magic_variable()

Usage

Users can now access the debugger directly in the Python console:

# After this change - dbg is automatically available
dbg.launch_and_wait()
dbg.step_into_and_wait()
dbg.regs['rax']

The dbg variable automatically:

• Updates based on the current binary view context
• Returns None when no active debugger context is available
• Provides the same functionality as manually created DebuggerController instances

Implementation

The implementation adds 8 lines of code to api/python/debuggercontroller.py:

def _get_debugger(instance: binaryninja.PythonScriptingInstance):
    if instance.interpreter.active_view is None:
        return None
    return DebuggerController(instance.interpreter.active_view)

binaryninja.PythonScriptingProvider.register_magic_variable(
    "dbg",
    _get_debugger
)

This follows the exact same pattern as other Binary Ninja magic variables and integrates seamlessly with the existing scripting infrastructure.

Fixes #851.

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