Upgrade to Rust 1.86

[devin-ai-integration]

Upgrades the rust-toolchain to 1.86 and fixes clippy warnings that emerged from the upgrade.

• Updated rust-toolchain from 1.80 to 1.86
• Fixed needless lifetimes in iterator and octet implementations
• Replaced manual div_ceil implementations with the built-in method
• Changed a large const array to static
• Added type annotations to size variables in tests

The 'just test' command passes successfully.

Link to Devin run: https://app.devin.ai/sessions/8619778a529f44499b6b50a927e25a69

[devin-ai-integration]

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