docs: add Rust rewrite feasibility issue draft

[DU4DAMA]

Motivation

• Assess the feasibility, cost, and risks of replacing all Go code in the repository with Rust by mapping the current codebase and Rust ecosystem alternatives.
• Surface the largest migration blockers (SQLite driver/DB abstraction, JS VM plugin system, and Go library embedding model) and estimate work effort and phases.
• Provide maintainers a concise in-repo Issue draft to kick off discussion and to recommend safer alternatives (PoC, partial Rustization, or keep Go mainline).

Description

• Added docs/issues/rust-rewrite-feasibility.md, a comprehensive Chinese draft Issue that documents repository metrics (44 packages, 442 Go files, ~37.9k prod LOC / ~56.6k test LOC), hotspots (core/, tools/, apis/, plugins/jsvm/) and the Go-native integration points.
• Mapped major capability domains to Rust crate options (e.g. axum/tokio/tower-http, rusqlite/sqlx, clap, oauth2, boa_engine/rquickjs, lettre, image, opendal) and explained where one-to-one replacements do not exist (notably dbx, modernc.org/sqlite semantics and goja+goja_nodejs behavior).
• Provided phased work estimates (PoC, core, API, files, scripts, testing/release), rough engineering effort estimates (roughly 60–100 engineer-weeks for a feature-aligned rewrite; 18–30 engineer-months to reach parity with high confidence), clear recommendations against a full-mainline rewrite, and proposed next steps (2–4 week PoC or targeted Rustization of hot paths).
• Committed the draft with the message docs: add Rust rewrite feasibility issue draft so maintainers can open/adjust the content as a GitHub Issue or ADR.

Testing

• Ran git diff --check to validate there are no whitespace/format errors in the change, and it completed successfully.
• Verified the change was staged and committed using git status --short and git rev-parse --short HEAD, and confirmed a new commit was created; no unit-test changes were required for this documentation-only addition.

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Codex Task