Use <lttng/lttng.h> in lttngpy and clean up includes (backport #222)

[mergify]

Description

This PR updates lttngpy to use the recommended umbrella LTTng header:

#include <lttng/lttng.h>

instead of including individual LTTng headers (domain.h, event.h, lttng-error.h, etc.).

Changes:

• Replace groups of LTTng includes in lttngpy .cpp files with <lttng/lttng.h>.
• Clean up redundant includes in corresponding .cpp files.
• Fix uncrustify style in snapshot.cpp so lttngpy tests pass.

No functional behavior changes are intended; this is an include/style cleanup.

Fixes #220

Is this user-facing behavior change?

Did you use Generative AI?

Additional Information

---

This is an automatic backport of pull request #222 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 91ff616 has failed:

On branch mergify/bp/kilted/pr-222
Your branch is up to date with 'origin/kilted'.

You are currently cherry-picking commit 91ff616.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   lttngpy/src/lttngpy/channel.cpp
	modified:   lttngpy/src/lttngpy/channel.hpp
	modified:   lttngpy/src/lttngpy/context_app.cpp
	modified:   lttngpy/src/lttngpy/context_lttng.cpp
	modified:   lttngpy/src/lttngpy/context_lttng.hpp
	modified:   lttngpy/src/lttngpy/context_perf.cpp
	modified:   lttngpy/src/lttngpy/context_perf.hpp
	modified:   lttngpy/src/lttngpy/event.cpp
	modified:   lttngpy/src/lttngpy/event.hpp
	modified:   lttngpy/src/lttngpy/session.cpp

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   lttngpy/src/lttngpy/snapshot.cpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[christophebedard]

Pulls: #231
Gist: https://gist.githubusercontent.com/christophebedard/2c7c7c6fe9a4311c4a852731acf2a372/raw/f8c1fc3f0d40f713896c57808e4a288cf72e2e51/ros2.repos
BUILD args: --packages-above-and-dependencies lttngpy
TEST args: --packages-above lttngpy
ROS Distro: kilted
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/18028

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[christophebedard]

There were tons of failures due to agent turnover, but I managed to find jobs that were retried and passed.