[RF][HS3] Patched ParamHistFuncs | Minor clean up

[Phmonski]

This Pull request:

• New features and improvements for HS3

Changes or fixes:

• Added RooEffProd Class
• Changed Flag handling: Exclude nbins from "parameter_points" and "const" from data "axes"
• New Streamer/Factory Class for ParamHistFunc
• ParamHistFunc now accepts custom modifiers
• Code clean up

[github-actions]

Test Results

    21 files      21 suites   3d 19h 54m 55s ⏱️
 3 748 tests  3 746 ✅ 0 💤 2 ❌
76 780 runs  76 773 ✅ 5 💤 2 ❌

For more details on these failures, see this check.

Results for commit 05dc574.

[TomasDado]

Hello, if possible, could this the changes in this code, once merged, be propagated to 6.38? These fixes are needed to publish the full likelihood in one of the ATLAS analysis, and we want to use a tagged version of the code for this.