Validate legacy error response statuses

[RAprogramm]

Summary

• validate ErrorResponse::new_legacy status codes before constructing responses
• reuse the provided message without cloning when the status is valid or invalid
• add regression coverage for both valid and fallback code paths of the legacy constructor

Testing

• cargo +nightly fmt --
• cargo +1.90.0 clippy -- -D warnings
• cargo +1.90.0 build --all-targets
• cargo +1.90.0 test --all
• cargo +1.90.0 doc --no-deps
• cargo audit
• cargo deny check

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https://chatgpt.com/codex/tasks/task_e_68d77de97238832ba4497b48b5fc64bb

[chatgpt-codex-connector]

💡 Codex Review

masterror/src/response/legacy.rs

Line 16 in a1119ad

pub fn new_legacy(status: u16, message: impl Into<String>) -> Self {

[P1] Restore alloc::String import for no_std builds

The diff drops use alloc::string::String, but new_legacy still uses impl Into<String>. That compiles with the default std feature because the standard prelude re‑exports String, yet the crate explicitly supports no_std (#![cfg_attr(not(feature = "std"), no_std)]). When consumers build with --no-default-features, String is no longer in scope and this module fails to compile. Reintroduce the alloc::string::String import or fully qualify the type so the function remains usable in no_std configurations.

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