This is needed for clangd LSP working properly.

Add struct `CameraSettings` which is supposed to hold all configurable
settings of the cameras (currently frame rate and the path to the pylon
settings file).
Further add functions to get default values and to load from TOML files.

To avoid having to either pass around the path to the TOML file in
higher-level scripts or to assume a hard-coded default path, use an
environment variable TRICAMERA_CONFIG_FILE to specify the path.

Note: This commit only adds the struct but does not yet use it.  It is
the first step in getting rid of the hard-coded frame rate.

I realised that frame rate and the pylon settings file are actually used
by different classes (TriCameraDriver and PylonDriver), so having them
together in one structure was a bit messy.

This commit rewrites the settings implementation to use a separate
struct for each module/class that needs configuration but still bundles
the loading in one central `Settings` class.

Configuration for the different classes is expected to be in separate
sections of the same TOML file:

```toml
[pylon_driver]
pylon_settings_file = "path/to/pylon_settings_file.txt"

[tricamera_driver]
frame_rate_fps = 10
```

While the TOML file is parsed as a whole in the constructor, the structs
for the different sections are only instantiated on demand, when the
corresponding getter is called.

Use `Settings` to get path to the Pylon settings file.

Expect a `Settings` instance as argument (optional, by default use the
"load file from env variable"-constructor).
Use it to set the `rate` at which images are fetched.
Also pass it on to PylonDriver instances, so the file is only read once.

This now technically allows to change the frame rate of the
TriCameraDriver.  Note however, that currently the rate of 10Hz is still
assumed in some other parts of the code, so changing it via the
configuration may not yet work properly in all cases.

Move the code for connecting to a Pylon camera out of the constructor of
PylonDriver to a standalone function.  This allows reusing the code.

While doing this, I noticed that the steps to open the camera and start
grabbing images where accidentally done in the `else`-block handling the
case when a DeviceUserID is specified.  I remember that connecting to a
camera without user id did work in the past, probably due to that.
Moving the relevant function calls out of the if/else should fix it.

This is a simple tool to load the current settings of a Pylon camera and
print it to stdout (so it can be piped into a file).
This makes it easier to produce a new Pylon settings file for use with
PylonDriver.

The previous implementation seemed to assume a hard-coded frame rate of
10 fps.  This wasn't even correct as PylonDriver uses the camera frame
rate which is configured via the Pylon settings file (currently 100fps).

Instead add a parameter "--update-freq" (still defaulting to 10) and use
that to compute the sleep duration of `cv2.waitKey`.
Behaviour should be mostly the same as before (with default values, the
sleep duration just changes from 90 to 100) but no explicit camera frame
rate is assumed anymore.

Add some more context to the error message that is shown
when parsing the configuration file fails.

Add fmt library for more convenient string formatting.

According to the
[documentation](https://docs.ros.org/en/humble/How-To-Guides/Ament-CMake-Documentation.html#installing),
those macros are not needed for target-based installs and should thus
normally not be used anymore.

Add a script that fetches TriCamera observations to analyse the frame
rate.  This is mostly meant for developers (for testing/debugging) but
might also be useful for users to verify their settings are loaded
correctly.