Update Rust toolchain from 1.85.0 to 1.86.0 with backward compatibility

[Copilot]

This PR updates the default Rust toolchain version from 1.85.0 to 1.86.0 in the GitHub Action workflow setup while maintaining backward compatibility for existing CI workflows.

Changes Made

• Updated the default value for the rust-toolchain input parameter from "1.85.0" to "1.86.0"
• Updated the description text to reflect the new default version
• Added installation of Rust 1.85.0 toolchain alongside existing 1.81.0 for backward compatibility

Backward Compatibility

The action now installs multiple Rust toolchain versions to ensure compatibility with older CI workflows:

• 1.86.0 - New default toolchain for new workflows
• 1.85.0 - Previous default, maintained for existing workflows that may depend on it
• 1.81.0 - Older version maintained for legacy compatibility

What's Not Changed

• All other configuration and setup steps remain unchanged
• YAML syntax and structure validated to ensure correctness
• Users can still override the default version by explicitly setting the rust-toolchain parameter

This ensures a smooth transition where existing workflows continue to work without modification while new workflows benefit from the latest Rust toolchain.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[marosset]

@copilot can you update this to also install rust 1.85 toolchain to maintain compatibility with older CI workflows?

Example: we still install the 1.81.0 toolchain here:

ci-setup-workflow/action.yml

Lines 146 to 151 in 3ababd8

	# We do this in case there is toolchain skew between repos
	- name: Install older rust toolchain(s)
	if: ${{ (runner.os == 'Linux') }}
	run: |
	rustup toolchain install 1.81.0
	shell: bash

[Copilot]

@copilot can you update this to also install rust 1.85 toolchain to maintain compatibility with older CI workflows?

Example: we still install the 1.81.0 toolchain here: https://github.com/hyperligh...

Added installation of Rust 1.85.0 toolchain alongside the existing 1.81.0 installation for both Linux and Windows platforms to maintain backward compatibility with older CI workflows. This ensures any workflows depending on 1.85.0 will continue to work after the default is updated to 1.86.0. (5f0cd30)

[marosset]

Let's merge https://github.com/hyperlight-dev/dev-images/pull/35 and build new images, then get this in