trx_toolkit: Move FakeTRX-related performance-sensitive modules to Cython

Cython (https://cython.org/ , https://cython.readthedocs.io/en/latest/)
is Python-compatible compiled language, that extends Python and allows
to add type annotations which help to optimize generated code. It is
based on Pyrex (https://www.csse.canterbury.ac.nz/greg.ewing/python/Pyrex/)
which is no longer actively maintained this days.

Using Cython allows one to take Python codebase and improve its speed
incrementally step by step instead of doing full rewrite from scratch.

Here we are only hooking Cython build system into the project and move
*.py to *.pyx files for the following modules:

	- burst_fwd.c
	- _clck_gen.c
	- data_if.c
	- data_msg.c
	- _fake_trx.c
	- udp_link.c
	- transceiver.c

Those modules turned up to require being optimized because their
functionality is used by fake_trx loop non-stop at the very least ~2000
times a second if there is only one BTS attached to fake_trx.

We will optimize those modules step by step in the follow-up patches.
For now it is only plain code movement with adding

	# cython: language_level=3

comment to the top of each file because else Cython uses 3str language
mode and emits a warning. We use language_level=3 because it has the
same semantic as of regular Python3.

The project now needs to be build before running: either `pip install -e .`
or `python setup.py build_ext -i` when doing development, or simple
`pip install .` for non-develop build.

There is no performance increase just from the move to Cython. We will
add optimizations step by step in the follow-up patches.

Change-Id: I2159a07bece13bda4f6ccd957063d4644d8b5e4f
---
M src/target/trx_toolkit/.gitignore
R src/target/trx_toolkit/_clck_gen.pyx
R src/target/trx_toolkit/_fake_trx.pyx
R src/target/trx_toolkit/burst_fwd.pyx
R src/target/trx_toolkit/data_if.pyx
R src/target/trx_toolkit/data_msg.pyx
A src/target/trx_toolkit/pyproject.toml
A src/target/trx_toolkit/setup.py
R src/target/trx_toolkit/transceiver.pyx
R src/target/trx_toolkit/udp_link.pyx
10 files changed, 35 insertions(+), 0 deletions(-)