chore(ci): make Rustup mirror configurable via build args

[fslongjin]

• Add RUSTUP_DIST_SERVER and RUSTUP_UPDATE_ROOT as ARG in Dockerfile
• Change hardcoded ENV values to reference ARG variables
• Allow CI workflows to override with official Rust servers ( https://static.rust-lang.org))

[github-actions]

Claude finished @fslongjin's task in 2m 26s —— View job

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PR #92 Review: Make Rustup mirror configurable via build args

• Gather context and read changed files
• Check DCO compliance
• Review code quality, bugs, security, and performance
• Post inline review comments
• Final summary

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DCO Check

The commit includes Signed-off-by: jinlong <jinlong@tencent.com> — DCO compliant.

Summary

This is a clean, well-structured PR that makes the Rustup mirror configuration overridable via Docker build args. The approach is correct and follows Docker best practices:

• Default values in the Dockerfile preserve backward compatibility (defaults to rsproxy.cn mirrors)
• CI overrides use the official static.rust-lang.org servers, which makes sense for GitHub Actions runners that have direct internet access
• Minimal, focused changes — only what's needed, no unnecessary refactoring

Findings

Category	Finding	Severity
Behavior	The rustup installer (sh.rustup.rs) on line 110-111 runs before the ENV instruction, so it won't use the custom mirror. This is fine because --default-toolchain none means no toolchain is downloaded at install time — the heavy downloads happen in the subsequent RUN block which correctly sees the ENV vars. See inline comment for a future-proofing tip.	Info
Style	The two standalone ENV lines (113-114) could be folded into the existing multi-line ENV block for consistency, though keeping them separate has readability benefits too.	Info
Security	No concerns — URLs are hardcoded in both Dockerfile and workflow files, no credentials involved.	N/A
Performance	No impact — the same number of downloads occurs, just from different servers.	N/A

Overall: This PR looks good. No blocking issues found.

[github-actions]

Minor style note: the ENV block above (lines 17-30) uses the multi-line \ continuation format. These two standalone ENV lines could be folded into that block for consistency, since they're all just setting environment variables:

ENV LANG=C.UTF-8 \
    LC_ALL=C.UTF-8 \
    ... \
    RUSTUP_DIST_SERVER="${RUSTUP_DIST_SERVER}" \
    RUSTUP_UPDATE_ROOT="${RUSTUP_UPDATE_ROOT}"

This is purely a style preference — the current approach is also valid and keeps the rustup-related config visually separate, which has its own readability benefit. Just flagging for consideration.