Dependencies cleanup

[tiffany352]

• Set default-features=false where applicable
• Use specific num libraries instead of the top-level crate, as some parts like complex numbers are not used.
• Replace reqwest with curl, which links the system libcurl and libssl when possible.
• Add opt-level="z" and enable LTO for release builds.

All these changes combined, the CLI binary goes from 10.7 megabytes (or 8.7 manually stripped) to 5.4 megabytes.

The wasm binary is unaffected, still around 2.3 megabytes.