Update rust-toolchain

[wks]

Currently, as of 8 Nov 2022, the file mmtk-core/rust-toolchain locks the Rust toolchain version to 1.59.0, but the latest stable Rust toolchain is 1.65.0. This means the toolchain we use is now 9 months behind the latest stable.

Locking the toolchain version has certain advantages, such as

• If it is tested on the CI, it probably works on other machines because they use the same compiler.
• The performance comparison between mmtk-core revisions is consistent because they use the same compiler.

However, the problems include

• Some programs may break on newer toolchain versions, because
  • The language semantics or standard library may change, deprecating old features, or
  • Newer compilers may have different behaviour for programs with undefined behaviours.
    • (See Illegal instruction with Rust 1.65.0 #691)
• Some third-party library mmtk-core depends on require newer language or stdlib features.
  • (See this line and this PR comment)
• Newer cargo clippy can provide warnings of more smelly code than before.

Before we bump the version, we need to:

• Fix bugs that break with the new toolchain
  • Illegal instruction with Rust 1.65.0 #691
• Update dependency versions.
  • enum-map = "=2.1" (newest version is 2.4.1)
• Fix (or suppress when necessary) new clippy warnings.
• (ANU-only) Ensure development and testing machines are equipped with the new toolchain.