refactor: Unify PrimitiveSlice and Scalaritem

[mehmetozsoy-synnada]

Description

Include a brief and concise description of the PR.

What is Changed

Include the changes introduced in this PR.

• __getitem__ of ExtendTemplate is updated
• PrimitiveSlice model is removed
• constraints of PrimitiveSlice is updated

Checklist:

• Tests that cover the code added.
• Corresponding changes documented.
• All tests passed.
• The code linted and styled (pre-commit run --all-files has passed).

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.75%. Comparing base (d62bce2) to head (a50e111).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
mithril/framework/constraints.py	93.33%	2 Missing ⚠️

@@            Coverage Diff             @@
##             main     #128      +/-   ##
==========================================
- Coverage   88.75%   88.75%   -0.01%     
==========================================
  Files          61       61              
  Lines       15502    15558      +56     
==========================================
+ Hits        13759    13808      +49     
- Misses       1743     1750       +7     

Files with missing lines	Coverage Δ
mithril/framework/common.py	96.68% <100.00%> (+0.12%)	⬆️
mithril/framework/logical/essential_primitives.py	99.55% <ø> (-0.02%)	⬇️
mithril/framework/logical/model.py	97.49% <100.00%> (+<0.01%)	⬆️
mithril/framework/physical/model.py	89.19% <100.00%> (+0.26%)	⬆️
mithril/framework/constraints.py	94.98% <93.33%> (-0.02%)	⬇️

... and 4 files with indirect coverage changes