tests: add Vec fuzz harness

Adds a basic fuzzing test harness using `cargo-fuzz` to run randomized tests
against the `Vec` type.

Author: 0xllx0

fuzz/.gitignore

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+target
+corpus
+artifacts
+coverage

fuzz/Cargo.toml

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+[package]
+name = "heapless-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[dependencies.heapless]
+path = ".."
+
+[[bin]]
+name = "fuzz_vec"
+path = "fuzz_targets/fuzz_vec.rs"
+test = false
+doc = false
+bench = false

fuzz/fuzz_targets/fuzz_vec.rs

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+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+
+use heapless::Vec;
+
+fn test_vec<const N: usize>(data: &[u8]) {
+    if let Ok(vec) = Vec::<u8, N>::from_slice(data) {
+        assert_eq!(vec.as_slice(), data);
+    }
+}
+
+fuzz_target!(|data: &[u8]| {
+    match data.len() {
+        0 => (),
+        len if len <= 16 => test_vec::<16>(data),
+        len if len <= 32 => test_vec::<32>(data),
+        len if len <= 64 => test_vec::<64>(data),
+        len if len <= 128 => test_vec::<128>(data),
+        len if len <= 256 => test_vec::<256>(data),
+        len if len <= 512 => test_vec::<512>(data),
+        len if len <= 1024 => test_vec::<1024>(data),
+        len if len <= 2048 => test_vec::<2048>(data),
+        len if len <= 4096 => test_vec::<4096>(data),
+        _ => (),
+    }
+});