Proctree improvements (cont)

[geyslan]

Continuation of #4540

Close: #4546

Ran these in main and proctree-the-third branches:

dist/tracee --metrics --pyroscope --pprof -s tree=2609608 -e sched_process_exec,sched_process_fork,sched_process_exit --proctree source=both --proctree disable-procfs -o none
dist/tracee --metrics --pyroscope --pprof -s tree=2241901 -e sched_process_exec,sched_process_fork,sched_process_exit --proctree source=both -o none

Stressor details:

Details
8 threads with 1_000_000 ops each running on:

cpu: AMD Ryzen 9 7950X 16-Core Processor
MemTotal: 64923992 kB (64GB)

procfs disabled

| Metric       | main              | proctree-the-third | % Diff (main vs. work)  |
|--------------|-------------------|--------------------|-------------------------|
| malloc avg   | 1,667,695         | 1,622,511          | -2.7%                   |
| heap avg     | 103MB             | 85MB               | -17.5%                  |
| heap obj avg | 752,513           | 685,354            | -8.9%                   |

procfs enabled

| Metric       | main.             | proctree-the-third | % Diff (main vs. work)  |
|--------------|-------------------|--------------------|-------------------------|
| malloc avg   | 2,097,349         | 2,015,099          | -3.9%                   |
| heap avg     | 189MB             | 136MB              | -28.0%                  |
| heap obj avg | 1,265,703         | 1,151,860          | -9.0%                   |

1. Explain what the PR does

1150c94 chore(proctree): use atomic types
989290e perf(proctree): centralize child and thread Maps
ecba829 perf(proctree)!: rearrange struct fields

989290e perf(proctree): centralize child and thread Maps

Previously, each Process maintained its own maps for children and
threads, leading to significant overhead in the process tree. This
commit moves those maps into the ProcessTree, which now centrally
manages the children and threads for every process.

Additionally, this change allows us to simplify the Process struct by
removing the dedicated mutex that was solely used for protecting the
individual maps.

ecba829 perf(proctree)!: rearrange struct fields

Mind the padding and the alignment of the fields to avoid wasting
memory.

BREAKING CHANGE: invoked_from_kernel, sched_process_exec event arg, is
now a bool.

2. Explain how to test it

3. Other comments

[rscampos]

LGTM

[geyslan]

/fast-forward