Enhance test_egg_substitution_fx_xyz to cover symmetry, transitivity, congruence, and substitution

[Copilot]

Plan to Fix test_egg_substitution_fx_xyz

• Understand the issue and current test structure
• Modify test_egg_substitution_fx_xyz to be more comprehensive by combining:
  • Symmetry: test that a=b derives b=a
  • Transitivity: test that a=b, b=c derives a=c
  • Congruence: test that b=c derives f(b)=f(c)
  • Substitution: test that f(a), a=c derives f(c)
• Run tests to validate the changes work correctly
• Verify the test is more complex and comprehensive as requested
• Fix pre-commit formatting issues

Original prompt

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This section details on the original issue you should resolve

<issue_title>egg的测试的倒数第二个例子不合适</issue_title>
<issue_description>test_egg_substitution_fx_xyz这个需要修改得复杂点。

现在这个不合适，应该把前面几个综合起来测试，现在缺了a=b得到b=a和test_egg_congruence_fx_fy</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes egg的测试的倒数第二个例子不合适 #29

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[hzhangxyz]

@copilot 修一下pre commit的问题

[Copilot]

Pull request overview

This PR enhances the test_egg_substitution_fx_xyz test to comprehensively validate the integration of four core egraph equality rules (symmetry, transitivity, congruence, and substitution) rather than testing only a simple substitution chain.

• Replaced simple variable chain test (x=y, y=z, f(x) → f(z)) with an integrated scenario using a, b, c variables
• Added verification for symmetry (a=b → b=a), transitivity (a=b, b=c → a=c), congruence (b=c → f(b)=f(c)), and substitution (f(a), a=c → f(c))
• Enhanced test assertions from one to four, checking each egraph rule individually

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[Copilot]

@copilot 修一下pre commit的问题

Fixed in commit 90d629b. The pre-commit formatter removed trailing whitespace from the docstring (lines 136 and 141). All pre-commit checks now pass.