Internal Templates Loader/Parser caches refactoring

[Mzack9999]

Proposed changes

This PR implements the following changes:

• Group together (not very elegantly) all templates related code within the pkg/templates/ package to minimize circular import scenarios and redundant logic
• parsers package has been moved from static to struct and linked to ExecuterOptions, in this way multiple executions will still benefit of the cache, but will be cleared out when the initial object go out of scope. Ref: running nuclei with sdk may have gc problem #4836
• Structures such asTagFilter are referenced everywhere within the code, and makes it nearly impossible to refactor the internal package tree consistently because Template entity, originally supposed to persist in memory, is tied to runtime execution options. This has been moved and the import loop "hidden" via runtime casting, allowing to reduce Templates to ExecuterOptions scope.

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)

[tarunKoyalwar]

lgtm !