By making the stopping loop the first loop, we can avoid using `pyo3/allow_threads`, which
seems buggy.

This commit is an initial draft at fixing #147. The error is due to the
fact that pyo3 has linked the libpython from the compilation and not
trying to use libpython that is available in `LD_LIBRARY_PATH`.

The current only solution to disable the linking is to use the `extension-module` flag.
This requires to make the python `runtime-node` packaged in a python library.
The python `runtime-node` should also be fully compatible with the other operators in case we want hybrid runtime.

The issue that i'm facing is that. Due to the packaging, I have to deal with the `GIL` that is present from the start of
`dora-runtime` node. This however makes the process single threaded wich is impossible.

So, I have to disable it, but when I do, I have a race condition:
```bash
Exception ignored in: <module 'threading' from '/usr/lib/python3.8/threading.py'>
Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 1373, in _shutdown
    assert tlock.locked()
AssertionError:
```
The issue is the same as https://github.com/PyO3/pyo3/issues/1274

To fix this issue, I'm going to look again at the different step to make this work.

But this is my current investigation.

Implement a C++ operator API

Useful in case of emergencies.

Create C++ node API library

Based on Rust API using `cxx` for bridging.

* Changing `drop_operator` to `__del__` in `python.rs`

Using the default python destructor function for dora operator simplify
the usability of dora as user does not have to learn as many custom
methods.

This also creates a symmetry with __init__ and  reduce the risk of
errors if drop_operator is not present or misspelled.

It also enables the usability of dora operator outside of dora ( for
testing dor example ) and let it be naturally garbage collected.

* fixing clippy and add comments

* fix formatting

Fix warnings

* add opentelemetry feature to python op

* modify `python-dataflow` to test opentelemetry

* change `timer` topic to `tick`

* adding tracing to `shared_libraries`

* example install refactoring

* Rename `input` to `dora_input` for python ex

Start creating command line interface with `check`, `build`, `graph` and `templates` commands

Changes the message format from raw data bytes to a higher-level `Message` struct serialized with capnproto. In addition to the raw data, which is sent as a byte array as before, the `Message` struct features `metadata` field. This metadata field can be used to pass open telemetry contexts, deadlines, etc.

To make it usable for other projects.

Make dora and its examples work on Windows and macOS

Otherwise we might cause a null pointer segfault.