test: Use eqeqeq and no-template-curly-in-string

[samestep]

Description

This PR enables the ESLint rules eqeqeq and no-template-curly-in-string at the "error" level in @penrose/core. I chose these specific ones because they both revealed some code that actually should be changed, rather than just being stylistic or not surfacing any issues in our codebase at all.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new ESLint warnings
• I have reviewed any generated changes to the diagrams/ folder

[codecov]

Codecov Report

Merging #968 (3eb5a4e) into main (97d0e89) will increase coverage by 0.05%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##             main     #968      +/-   ##
==========================================
+ Coverage   63.17%   63.23%   +0.05%     
==========================================
  Files          62       62              
  Lines        7925     7918       -7     
  Branches     1843     1837       -6     
==========================================
  Hits         5007     5007              
+ Misses       2794     2790       -4     
+ Partials      124      121       -3     

Impacted Files	Coverage Δ
packages/core/src/contrib/Functions.ts	13.71% <0.00%> (ø)
packages/core/src/engine/Evaluator.ts	32.98% <0.00%> (+0.59%)	⬆️
packages/core/src/renderer/AttrHelper.ts	53.61% <0.00%> (ø)
packages/core/src/contrib/Queries.ts	100.00% <100.00%> (ø)

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[cmumatt]

Glad we are getting errors for these now. Thanks for doing this!