Allow Nodes::Nodes to hold arbitrary values

[gonzedge]

Allow Nodes::Nodes to hold arbitrary values! Now, you can have a terminal node that on top of representing its word, it can hold on to

• Add value attribute to Nodes::Node
• Add optional, nilable value argument to Container#add, Nodes::Node#add
• Store given value in terminal node via Nodes::Raw#add and Nodes::Raw#add_to_children_tree, when present
• Update Compressor#merge and Compressor#compress_children_and_copy to store value from Nodes::Raw in the
  terminal Nodes::Compressed, when present
• Add optional values array argument to Container#concat corresponding 1:1 to words, that passes each word and
  value to #add when present
• Add value to Inspectable#inspect output, when present
• Add generic type TValue to Nodes::Node type signature
  • Extract _Nilable interface to own top-level file
  • Make value attribute in Nodes::Node use the new TValue generic type
  • Allow TValue to be nil by default with ?
  • Require TValue to implement _Inspect built-in(!) interface, for Inspectable module
  • Change all types that depend on Nodes::Node also have the generic type TValue < _Inspect
    including static methods
  • Add optional TValue argument to Container#add, Nodes::Node#add, and Nodes::Raw#add_to_children_tree
  • Add optional Array[TValue?] argument to Container#concat
  • Add new || raises because the inline type conversion to non-nil doesn't work anymore for steep check 🤷🏻‍♂
• Make compatible with rbs v3.7.0 and steep v1.9.0
  • Change ProviderCollection#[] to return TProvider?
  • Change Nodes::Node#[] to return Nodes::Node[TValue]?
  • Change Container#[] to return Nodes::Node[TValue]?
  • Add type annotations for UnannotatedEmptyCollections
  • Raise InvalidOperations when compress(child) return nil value which is not supposed to be possible

[codeclimate]

Code Climate has analyzed commit b9fcac1 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (95% is the threshold).

This pull request will bring the total coverage in the repository to 100.0% (0.0% change).

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