fix(userspace/libsinsp): assorted pass-by-reference performance optimizations

[jasondellaluce]

What type of PR is this?

/kind cleanup

Any specific area of the project related to this PR?

/area libsinsp

Does this PR require a change in the driver versions?

What this PR does / why we need it:

When looking at performance profiles of Falco, I discovered that we unwillingly pass variables by value more than needed. Specially with shared pointers, we occasionally prevent compilers from inlining and eliding reference counting that causes a non-negligible cost when running on high event throughput. At the same time, we use shared pointers even when not needed on internal functions.

Which issue(s) this PR fixes:

Special notes for your reviewer:

/milestone 0.18.0

Does this PR introduce a user-facing change?:

fix(userspace/libsinsp): assorted pass-by-reference performance optimizations

[github-actions]

Perf diff from master - unit tests

     6.71%     +2.00%  [.] sinsp::next
     5.12%     -1.91%  [.] sinsp_thread_manager::find_thread
     2.68%     +1.62%  [.] std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release
    10.30%     +1.33%  [.] sinsp_parser::reset
     4.11%     -1.10%  [.] sinsp_thread_manager::get_thread_ref
     4.12%     -0.86%  [.] sinsp_evt::load_params
     5.48%     -0.81%  [.] next
     3.43%     +0.76%  [.] gzfile_read
     1.43%     -0.67%  [.] sinsp_parser::event_cleanup
     1.11%     -0.53%  [.] std::vector<sinsp_evt_param, std::allocator<sinsp_evt_param> >::emplace_back<sinsp_evt*, unsigned int&, char const*, unsigned long&>

Perf diff from master - scap file

     9.70%     -4.59%  [.] 0x00000000000a77e0
    10.12%     -3.15%  [.] sinsp_filter_check_thread::extract_single
     2.53%     +1.82%  [.] sinsp_filter_check_event::extract_single
     2.48%     +1.81%  [.] sinsp_thread_manager::get_thread_ref
     2.57%     +1.75%  [.] sinsp::next
     5.04%     +1.67%  [.] std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char const*>
     7.57%     -1.58%  [.] sinsp_filter_check::get_field_info
     7.57%     -1.49%  [.] sinsp_filter_check::extract_nocache
     4.97%     -1.49%  [.] sinsp_filter_check::get_transformed_field_info
     4.96%     -1.48%  [.] sinsp_filter_check::apply_transformers

Heap diff from master - unit tests

total runtime: 0.13s.
calls to allocation functions: 9031 (70554/s)
temporary memory allocations: -10141 (-79226/s)
peak heap memory consumption: -160.08K
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Heap diff from master - scap file

total runtime: -0.02s.
calls to allocation functions: -3 (176/s)
temporary memory allocations: -9 (529/s)
peak heap memory consumption: -4.10K
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

[Andreagit97]

/approve

Thank you!

[poiana]

LGTM label has been added.

Git tree hash: e3cb6c12b70478f8ccb682ce4af0141be9fd4f94

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

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

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