Update toolchain to nightly-2025-05-09 (1.88)

[davidsemakula]

Description

This includes a bit more changes than a typical rustc nightly sync, some notable ones are

• Robust null pointer dereference analysis
  • Needed because of new explicit null pointer checks/assertions (i.e. AssertKind::NullPointerDereference) in MIR
• Equality expression refinement/simplification for casting and transmuting zero-value integers
  • This could have been a separate PR, but it's needed for the null pointer dereference analysis to be more precise
• Handling new Rvalue::Len operations
• Refactoring associated type normalization
• Handling (internal/experimental) unsafe binder types (Implement MIR lowering for unsafe binders rust-lang/rust#130514)

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• API change with a documentation update
• Additional test coverage
• Code cleanup or just keeping up with the latest Rustc nightly

How Has This Been Tested?

Ran ./validate.sh

Checklist:

• Fork the repo and create your branch from main.
• If you've added code that should be tested, add tests.
• If you've changed APIs, update the documentation.
• Ensure the test suite passes.
• Make sure your code lints.

[davidsemakula]

Hi @peter-cg
Sorry for the ping.
Just want to know if anyone is still reviewing these.
Thanks!