Fix convergence problem due to unbounded growing of assertion tree

[sonalmahajan15]

This PR fixes the convergence issues causes by unbounded growing of assertion trees with assignments in a loop, such as in the simple example shown below.

func test() {
         a := &A{}
	for {
		a = a.f
	}
}

Here, the assertion tree should look like root -> varAssertionNode (a) -> fldAssertionNode (f). However, the assertion before was growing unboundedly (root -> a -> f -> f -> f -> ...) until the stableRoundLimit was hit. This simple function was taking 7 iterations to converge, while after the code change it now takes only 3 iterations to converge.

Taking this opportunity, I have also added tests for testing fixpoint convergence. For this, I refactored existing infrastructure for anonymous functions and generalized it.

Note: the goal of this PR is to improve performance only, and should not have any effect on the reported errors.

[codecov]

Codecov Report

Attention: Patch coverage is 92.68293% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 87.55%. Comparing base (fe712a8) to head (8e70917).

Files	Patch %	Lines
assertion/function/assertiontree/backprop.go	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #244      +/-   ##
==========================================
+ Coverage   87.50%   87.55%   +0.04%     
==========================================
  Files          61       62       +1     
  Lines        7798     7828      +30     
==========================================
+ Hits         6824     6854      +30     
  Misses        796      796              
  Partials      178      178              

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[github-actions]

Golden Test

Note

✅ NilAway errors reported on standard libraries are identical.

3296 errors on base branch (main, fe712a8)
3296 errors on test branch (1d7f65a)

[yuxincs]

Nice find and great refactor for test helpers!