Upgrade stable branch to Rust 1.86.0 (#3985)

Advance the stable branch to fe0d9d2 and use the 1.86.0 channel.

Additional Details:
- The 1.86.0 release was branched from main on 2025-02-14 (see
https://releases.rs/docs/1.86.0/)
- The latest commit on main with a close toolchain is fe0d9d2 which
upgraded the toolchain to 2025-02-12. The next commit upgrades the
toolchain to 2025-02-21, which doesn't compile without reverting some of
the changes done in that commit.
- Based on the previous point, I picked fe0d9d2, and made an
additional change to make it compatible with the 1.86.0 release:
```diff
diff --git a/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs b/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
index 8606196..0c2a81c 100644
--- a/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
+++ b/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
@@ -667,7 +667,7 @@ fn codegen_rvalue_aggregate(
                 assert!(operands.len() == 2);
                 let typ = self.codegen_ty_stable(res_ty);
                 let layout = self.layout_of_stable(res_ty);
-                assert!(layout.ty.is_unsafe_ptr());
+                assert!(layout.ty.is_raw_ptr());
                 let data = self.codegen_operand_stable(&operands[0]);
                 match pointee_ty.kind() {
                     TyKind::RigidTy(RigidTy::Slice(inner_ty)) => {
```
(the same change was made in the next commit that upgraded the toolchain
to 2025-02-21)

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

---------

Signed-off-by: Felipe R. Monteiro <felisous@amazon.com>
Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: Felipe R. Monteiro <felisous@amazon.com>
Co-authored-by: Rémi Delmas <remi.delmas.3000@gmail.com>
Co-authored-by: Remi Delmas <delmasrd@amazon.com>
Co-authored-by: Celina G. Val <celinval@amazon.com>
Co-authored-by: Felipe R. Monteiro <rms.felipe@gmail.com>
Co-authored-by: Qinheping Hu <qinhh@amazon.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: tautschnig <1144736+tautschnig@users.noreply.github.com>
Co-authored-by: rajath-mk <rjkotyal@amazon.com>
Co-authored-by: Carolyn Zech <cmzech@amazon.com>
Co-authored-by: Michael Tautschnig <tautschn@amazon.com>
Co-authored-by: Michael Tautschnig <mt@debian.org>
Co-authored-by: thanhnguyen-aws <ntson@amazon.com>
Co-authored-by: carolynzech <71352687+carolynzech@users.noreply.github.com>

Author: 12 people

CHANGELOG.md

@@ -4,6 +4,23 @@ This file contains notable changes (e.g. breaking changes, major changes, etc.)
 
 This file was introduced starting Kani 0.23.0, so it only contains changes from version 0.23.0 onwards.
 
+## [0.59.0]
+
+### Breaking Changes
+* Deprecate `--enable-unstable` and `--restrict-vtable` by @celinval in https://github.com/model-checking/kani/pull/3859
+* Do not report arithmetic overflow for floating point operations that produce +/-Inf by @rajath-mk in https://github.com/model-checking/kani/pull/3873
+
+### What's Changed
+* Fix validity checks for `char` by @celinval in https://github.com/model-checking/kani/pull/3853
+* Support verifying contracts/stubs for generic types with multiple inherent implementations by @carolynzech in https://github.com/model-checking/kani/pull/3829
+* Allow multiple stub_verified annotations, but check for duplicate targets by @remi-delmas-3000 in https://github.com/model-checking/kani/pull/3808
+* Fix crash if a function pointer is created but never used by @celinval in https://github.com/model-checking/kani/pull/3862
+* Fix transmute codegen when sizes are different by @celinval in https://github.com/model-checking/kani/pull/3861
+* Stub linker to avoid missing symbols errors by @celinval in https://github.com/model-checking/kani/pull/3858
+* Toolchain upgrade to nightly-2025-01-28 by @feliperodri @tautschnig
+
+**Full Changelog**: https://github.com/model-checking/kani/compare/kani-0.58.0...kani-0.59.0
+
 ## [0.58.0]
 
 ### Major/Breaking Changes