fs: allocate FSReqPromise stat arrays lazily #7888

Job	Run time
Build slim tarball	1m 27s
aarch64-linux: Cache V8 build	20s
x86_64-darwin: with shared libraries	35m 27s
aarch64-darwin: with shared libraries	26m 13s
x86_64-linux: with shared libraries	26m 37s
aarch64-linux: with shared boringssl-0.20260526.0	26m 28s
aarch64-linux: with shared openssl-3.5.6	25m 26s
aarch64-linux: with shared openssl-3.6.2	25m 53s
aarch64-linux: with shared openssl-3.0.20	24m 50s
aarch64-linux: with shared openssl-1.1.1w	25m 3s
aarch64-linux: with shared openssl-4.0.0	24m 27s
	4h 2m 11s

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