fix: undefined names in Python error paths

[Anai-Guo]

Fixes five NameErrors in Python code that only runs on error or optional paths, so they were never hit in normal use or CI. In each case the intended behaviour (log + exit, handle the NVML failure, raise a clear argument error, write to stdout) was replaced by a NameError.

file	problem	fix
Detray/tests/tools/python/options/common_options.py	--logfile path uses os.path / os.mkdir, but os is not imported	import os
Detray/tests/tools/python/options/plotting_options.py	unknown --output_format logs {out_format} (undefined) before sys.exit(1)	use args.output_format
Detray/tests/tools/python/propagation_benchmarks.py	except NVMLError — name never imported, so an NVML failure raises NameError from inside the handler	except nvidia_smi.NVMLError (nvidia_smi does from pynvml import *)
Detray/codegen/detray-sympy/detray_sympy/output.py	write_out_file(code) with no file name writes to sys.stdout, but sys is not imported	import sys
Python/Examples/python/odd.py	getOpenDataDetector(gen3=True, misaligned=True) raises undefined InvalidArgumentError	ValueError

Found with pyflakes. Verified by calling each function on the failing path, before and after:

before                                              after
common_options logfile: NameError 'os'              OK
plotting bad format:    NameError 'out_format'      SystemExit 1
write_out_file stdout:  NameError 'sys'             OK
nvml failure path:      NameError 'NVMLError'       handled (prints the NVML error)

(nvidia_smi.NVMLError checked against the nvidia-ml-py3 package: resolves to pynvml.NVMLError.) odd.py was reformatted by black 26.5.1, which collapsed the raise onto one line.

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