Adding memguardian + various optimizations

[Mzack9999]

Proposed changes

• Introducing the memguardian component that actively monitor used memory. Activation is optional via export MEMGUARDIAN=1. If the used RAM is above the threshold (default 75% of available RAM). It reduces parallel threading of templates to either MEMGUARDIAN_THREADS if defined, or 1/5 of the total original threading. Also if MEMGUARDIAN_ALLOC is defined, it caps the maximum amount of buffers that can be allocated in the pool. When memory conditions are back to normal, the slow down mechanisms are automatically reverted.
• collecting events within ScanContext is now optional, as it's not used anywhere and it was preventing gc to recycle large maps of data (and probably a co-cause of running nuclei with sdk may have gc problem #4836)

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Example

Closes #4756

$ MEMGUARDIAN=1 go run . -l 790targets.txt -jsc 110 -stats -tags fuzz,fuzzing,brute-force,bruteforce,brute,dos,local,code  -severity critical -rl 0
...
[INF] Templates loaded for current scan: 6
[INF] Executing 4 signed templates from projectdiscovery/nuclei-templates
[WRN] Executing 3 unsigned templates. Use with caution.
[INF] Targets loaded for current scan: 790
[0:00:06] | Templates: 6 | Hosts: 790 | RPS: 1796 | Matched: 0 | Errors: 0 | Requests: 11227/6737120 (0%)
...
[0:35:50] | Templates: 6 | Hosts: 790 | RPS: 686 | Matched: 0 | Errors: 37507 | Requests: 6417135/6737120 (95%)

[Mzack9999]

Optional behavior - Merging