refactor: smart pointer usage

[federico-sysdig]

What type of PR is this?
/kind cleanup

Any specific area of the project related to this PR?
No specific area.

What this PR does / why we need it:
There are some usages of smart pointers that can be simplified a but and, occasionally, made more efficient.

1. Use the overloaded dereference operator directly on the smart pointer without invoking get(), i.e. prefer *ptr rather than *(ptr.get()).
2. Create objects stored in smart pointers with make_unique or make_shared rather than using new. For shared_ptrs this has the performance advantage of storing the pointer's control block with the object itself, improving memory locality, beneficial for cache reasons, and using a single allocation call.
3. Prefer using automatic objects - i.e. stored on the stack - than heap allocated ones. This effectively removes the usage of the smart pointer.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[github-actions]

This PR may bring feature or behavior changes in the Falco engine and may require the engine version to be bumped.

Please double check userspace/engine/falco_engine_version.h file. See versioning for FALCO_ENGINE_VERSION.

/hold

[poiana]

LGTM label has been added.

Git tree hash: 5dc02d7a46f468ea47bc0189c2c2046dfdf348ad

[FedeDP]

/milestone 0.38.0

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[FedeDP]

/unhold