fix: dangling pointer and mixed-signedness warning

[federico-sysdig]

What type of PR is this?
/kind cleanup

Any specific area of the project related to this PR?
/area build
/area tests

Does this PR require a change in the driver versions?
No

What this PR does / why we need it:
Fixes an error when taking the address of a temporary string and a warning about mixed sign integer comparison with clang 18.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[github-actions]

Perf diff from master - unit tests

     9.97%     +3.25%  [.] sinsp_parser::reset
     2.82%     +3.02%  [.] sinsp_parser::process_event
    11.00%     -1.44%  [.] sinsp::next
     4.15%     -0.76%  [.] sinsp_evt::load_params
     1.98%     +0.50%  [.] is_conversion_needed
     1.40%     -0.46%  [.] sinsp_parser::event_cleanup
     4.16%     -0.45%  [.] gzfile_read
     8.03%     -0.44%  [.] sinsp_evt::get_type
     3.74%     +0.30%  [.] sinsp_thread_manager::find_thread
     0.69%     -0.27%  [.] scap_event_has_large_payload

Heap diff from master - unit tests

peak heap memory consumption: 0B
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Heap diff from master - scap file

peak heap memory consumption: 0B
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Benchmarks diff from master

Comparing gbench_data.json to /root/actions-runner/_work/libs/libs/build/gbench_data.json
Benchmark                                                         Time             CPU      Time Old      Time New       CPU Old       CPU New
----------------------------------------------------------------------------------------------------------------------------------------------
BM_sinsp_split_mean                                            +0.0343         +0.0343           144           149           144           149
BM_sinsp_split_median                                          +0.0353         +0.0353           144           149           144           149
BM_sinsp_split_stddev                                          -0.4993         -0.4996             1             1             1             1
BM_sinsp_split_cv                                              -0.5159         -0.5161             0             0             0             0
BM_sinsp_concatenate_paths_relative_path_mean                  -0.0694         -0.0694            61            56            61            56
BM_sinsp_concatenate_paths_relative_path_median                -0.0685         -0.0685            61            56            61            56
BM_sinsp_concatenate_paths_relative_path_stddev                -0.7131         -0.7129             1             0             1             0
BM_sinsp_concatenate_paths_relative_path_cv                    -0.6917         -0.6915             0             0             0             0
BM_sinsp_concatenate_paths_empty_path_mean                     +0.0161         +0.0161            23            24            23            24
BM_sinsp_concatenate_paths_empty_path_median                   +0.0156         +0.0156            23            24            23            24
BM_sinsp_concatenate_paths_empty_path_stddev                   -0.1503         -0.1483             0             0             0             0
BM_sinsp_concatenate_paths_empty_path_cv                       -0.1638         -0.1619             0             0             0             0
BM_sinsp_concatenate_paths_absolute_path_mean                  -0.1251         -0.1251            65            56            65            56
BM_sinsp_concatenate_paths_absolute_path_median                -0.1211         -0.1211            64            57            64            57
BM_sinsp_concatenate_paths_absolute_path_stddev                +1.7125         +1.7090             0             1             0             1
BM_sinsp_concatenate_paths_absolute_path_cv                    +2.1003         +2.0963             0             0             0             0
BM_sinsp_split_container_image_mean                            -0.0051         -0.0051           391           389           391           389
BM_sinsp_split_container_image_median                          -0.0091         -0.0091           392           388           392           388
BM_sinsp_split_container_image_stddev                          -0.1560         -0.1574             3             2             3             2
BM_sinsp_split_container_image_cv                              -0.1516         -0.1530             0             0             0             0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.44%. Comparing base (d1881b4) to head (fdbf6be).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2223   +/-   ##
=======================================
  Coverage   75.44%   75.44%           
=======================================
  Files         265      265           
  Lines       34057    34057           
  Branches     5801     5801           
=======================================
+ Hits        25694    25695    +1     
+ Misses       8363     8362    -1     

Flag	Coverage Δ
libsinsp	75.44% <ø> (+<0.01%)	⬆️

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[Andreagit97]

/approve

[poiana]

LGTM label has been added.

Git tree hash: e7723b39ac4ac62e3a83c282ce0656d8e995a053

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, FedeDP, federico-sysdig

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