refactor[lang]: remove VyperNode __hash__() and __eq__() implementations

[charles-cooper]

it is a performance and correctness footgun for the hash and eq implementations to recurse. for instance, two nodes from different source files should never compare equal (you can use deepequals to signal intention there).

i refactored the test suite by temporarily overriding the __ne__ implementation for VyperNode so that we can find all the != uses in the tests. the CI for this commit (0a9830b) passes (run https://github.com/vyperlang/vyper/actions/runs/12574333551/), and the training wheels are taken off in commit 71726ad.

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Commit message

it is a performance and correctness footgun for `VyperNode`'s hash and
eq implementations to recurse. for instance, two nodes from different
source files should never compare equal.

several tests rely on the recursive behavior of the eq implementation;
a utility function `deepequals()` is added in this PR so that tests
can perform the recursive check on AST nodes where needed. nowhere in
the compiler itself (`vyper/` directory) is the recursive definition
relied on.

this commit also slightly refactors the import analyzer so that uses
the new hash and eq implementations instead of the previous workaround
to avoid recursion (which was to use `id(module_ast)`.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.99%. Comparing base (f444c8f) to head (ee1d080).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4433      +/-   ##
==========================================
+ Coverage   91.98%   91.99%   +0.01%     
==========================================
  Files         119      119              
  Lines       16686    16673      -13     
  Branches     2808     2803       -5     
==========================================
- Hits        15348    15339       -9     
+ Misses        919      916       -3     
+ Partials      419      418       -1     

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