Adds disable ray tracing env var toggle.

[nathansizemore]

This has been verified locally to solve the NVIDIA crash with ray tracing params:

~/dev/zed 14:18:45
❯ cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.61s
     Running `target/debug/zed`
2026-02-05T14:18:50-05:00 INFO  [zed] ========== starting zed version 0.224.0+dev.4389ebb6f48562eb8432cfd85cca81e7b43dc88f, sha 4389ebb ==========

thread 'main' (167845) panicked at crates/gpui/src/platform/linux/platform.rs:84:17:
Unable to init GPU context
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

~/dev/zed 14:18:51
❯ BLADE_DISABLE_RAY_TRACING=1 cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.47s
     Running `target/debug/zed`
2026-02-05T14:19:14-05:00 INFO  [zed] ========== starting zed version 0.224.0+dev.4389ebb6f48562eb8432cfd85cca81e7b43dc88f, sha 4389ebb ==========
2026-02-05T14:19:15-05:00 WARN  [zed::reliability] Minidump endpoint not set
2026-02-05T14:19:15-05:00 INFO  [extension_host] extensions updated. loading 2, reloading 0, unloading 0
2026-02-05T14:19:15-05:00 WARN  [audio::audio_settings] Denoise does not work on debug builds, not enabling
2026-02-05T14:19:15-05:00 INFO  [gpui::platform::linux::platform] activate is not implemented on Linux, ignoring the call
2026-02-05T14:19:15-05:00 WARN  [audio::audio_settings] Denoise does not work on debug builds, not enabling
2026-02-05T14:19:15-05:00 INFO  [gpui::platform::blade::blade_renderer] Initializing Blade pipelines for surface SurfaceInfo { format: Bgra8Unorm, alpha: PreMultiplied }
2026-02-05T14:19:15-05:00 INFO  [workspace] Rendered first frame
2026-02-05T14:19:15-05:00 INFO  [zed::zed] Using GPU: GpuSpecs { is_software_emulated: false, device_name: "NVIDIA GeForce RTX 4070 Laptop GPU", driver_name: "NVIDIA", driver_info: "590.48.01" }
2026-02-05T14:19:15-05:00 INFO  [gpui::platform::blade::blade_renderer] Initializing Blade pipelines for surface SurfaceInfo { format: Bgra8Unorm, alpha: Ignored }

Fixes #295