Remove target-cpu=native from .cargo/config.toml for portable builds

[jose-compu]

Description

.cargo/config.toml sets rustflags = ["-C", "target-cpu=native"] for release builds. While this optimizes for the build machine, it produces binaries that may not run on other CPUs and can cause illegal instruction errors.

Proposed Changes

• Remove target-cpu=native from .cargo/config.toml
• Document it as an optional flag users can set locally for maximum performance
• Keep it only in a developer-facing profile or CI benchmark job if needed

Impact

Ensures published binaries and crates are portable.