refactor: add operators with addOperators in context constructor

[maxnowack]

Spreading the imports to objects converts them to plain objects again and resolves the issues discussed in #390
resolves #390

Update: see this comment

[codecov]

Codecov Report

Merging #391 (c90fcaa) into main (d17d517) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #391      +/-   ##
==========================================
- Coverage   98.75%   98.73%   -0.03%     
==========================================
  Files         290      290              
  Lines        4193     4195       +2     
  Branches      985      985              
==========================================
+ Hits         4141     4142       +1     
- Misses         46       47       +1     
  Partials        6        6              

Flag	Coverage Δ
unittests	98.73% <100.00%> (-0.03%)	⬇️

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Files	Coverage Δ
src/core.ts	100.00% <100.00%> (ø)

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[kofrasa]

Thanks for the PR @maxnowack. If copying the input resolves it, perhaps it would be better done within the operator register methods themselves to prevent other users from running into the same issue.

Consider updating useOperator and Context.addOperator functions instead if doing so would have the same effect.

Thoughts?

[maxnowack]

@kofrasa thanks for pointing me in this direction. I tried to verify this and realized that my reproduction environment wasn't up to date with the latest changes and that my proposed changes don't make sense at all.
The Context.addOperators (which is called by useOperators) method is already implicitly copying the object by looping over Object.entries.

My reproduction environment was using v6.4.7 instead of the latest changes on main. As I wasn't able to reproduce the TypeError with the latest changes, I rechecked the callstack of the error and saw the the call were not coming from useOperators but from Context.init.
The behavior how operators were loaded has changed with 254afa6 (here). As the context is now initialized with an empty object and the operators will be added explicitly with the corresponding methods, the TypeError is already fixed on main.

However, I just changed this PR to modify the Context.constructor to also use addOperators method internally. This ensures the copying of the operators regardless if the context were initialized with the operators or the operators were added after initialization.