DroneCAN DSDL compiler emits Python SyntaxWarning and deprecated CMake FindPythonInterp

[mrpollo]

Two sources of build noise from src/drivers/uavcan/libdronecan/:

pyratemp.py:273 has an invalid escape sequence '\#' that triggers a Python SyntaxWarning twice per board, ~20 times per CI job.

libuavcan/CMakeLists.txt:24 uses FindPythonInterp which CMake has removed (CMP0148). This fires 36 times in a single nuttx job.

Neither breaks the build today but CMP0148 will become a hard error in future CMake versions.

Example: https://github.com/PX4/PX4-Autopilot/actions/runs/22078615806/job/63799130549