Tens stagg fix

[mloubout]

Fix issue using Staggering object as input for staggered

[mloubout]

Note: This prevents sympy from forcing some weird type conversion because of

https://github.com/sympy/sympy/blob/16fa855354eb7bcabd3fe10993841e03b1382692/sympy/core/sympify.py#L414

That for example converts EnrichedTuples to sympy's tuples. By using _sympy_ explicitly it makes sure it only convert object with explicity conversion defined (so mostly pure sympy objects or our objects with it defined)

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.96%. Comparing base (df444ea) to head (a60b12a).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
devito/types/tensor.py	62.50%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2854   +/-   ##
=======================================
  Coverage   78.96%   78.96%           
=======================================
  Files         248      248           
  Lines       50950    50980   +30     
  Branches     4405     4411    +6     
=======================================
+ Hits        40232    40258   +26     
- Misses       9917     9919    +2     
- Partials      801      803    +2     

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