ci: clean before tools build (sanitizer leak), bump fuzz timeout to 15s #14

Job	Run time
ubuntu / clang / libfuzzer + asan (gguf reader, 30s)	1m 4s
ubuntu / aarch64 / qemu	29s
ubuntu / static checks (error uniqueness + include firewall)	4s
ubuntu / matmul microbenchmark (perf snapshot)	25s
ubuntu / clang / libfuzzer + asan (eosm reader, 30s)	1m 34s
ubuntu / cli lifecycle smoke (synthetic GGUF)	1m 11s
ubuntu / eosllm-server lifecycle smoke	9s
ubuntu / determinism (3-iteration bit-identical)	9s
macos-latest / clang / release	12s
windows-latest / gcc / debug	1m 12s
windows-latest / gcc / release	1m 20s
macos-latest / clang / debug	13s
ubuntu-latest / gcc / release	11s
ubuntu-latest / clang / release	14s
ubuntu-latest / clang / debug	11s
ubuntu-latest / gcc / debug	7s
ubuntu / clang / asan + ubsan + leaksan	28s
ubuntu / nightly all-checks (cron only)	0s
	9m 13s

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