fix(cfl): drop UBSan sanitizer — Rust has no -Z sanitizer=undefined

Rust's unstable -Z sanitizer flag accepts address, memory, thread, and
leak, but not 'undefined'.  UBSan is a C/C++ concept; there is no Rust
equivalent that satisfies OSS-Fuzz bad_build_check for the undefined
sanitizer job.  Remove 'undefined' from project.yaml sanitizers list
and the cflite_pr.yml matrix, and simplify build.sh back to a single
cargo fuzz build --release call (address-only).

https://claude.ai/code/session_01EJLZKDtcF1RGdKx6TcUTQG

Author: claude

.clusterfuzzlite/build.sh

@@ -1,18 +1,6 @@
 #!/bin/bash -eu
 
 cd "$SRC"/project
-
-SANITIZER="${SANITIZER:-address}"
-
-if [ "$SANITIZER" = "address" ]; then
-  cargo +nightly fuzz build --release
-elif [ "$SANITIZER" = "undefined" ]; then
-  # Rust has no UBSan equivalent via -Z sanitizer.
-  # Build without any sanitizer so bad_build_check sees no ASan instrumentation.
-  cargo +nightly fuzz build --sanitizer none --release
-else
-  cargo +nightly fuzz build --release
-fi
-
+cargo +nightly fuzz build --release
 find fuzz/target -maxdepth 4 -name 'fuzz_*' -executable \
   -not -name '*.d' -exec cp {} "$OUT"/ \;

.clusterfuzzlite/project.yaml

@@ -1,4 +1,3 @@
 language: rust
 sanitizers:
   - address
-  - undefined

.github/workflows/cflite_pr.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        sanitizer: [address, undefined]
+        sanitizer: [address]
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
       - uses: google/clusterfuzzlite/actions/build_fuzzers@884713a6c30a92e5e8544c39945cd7cb630abcd1 # v1