Update dependency rust-nightly to v2026-04-01 (#2939)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
-channel = "nightly-2026-02-15"
+channel = "nightly-2026-04-01"
 components = ["rustfmt", "clippy", "rust-src"]
 targets = ["aarch64-linux-android", "x86_64-linux-android"]
 profile = "minimal"