ICU-22991 Reduce fStamp to 8 bits #3307

Job	Run time
clang-valgrind-test	10m 22s
clang-valgrind-intltest (utility)	6m 27s
clang-valgrind-intltest (normalize)	6m 41s
clang-valgrind-intltest (collator)	5m 28s
clang-valgrind-intltest (regex)	5m 53s
clang-valgrind-intltest (format)	16m 13s
clang-valgrind-intltest (translit)	6m 16s
clang-valgrind-intltest (rbbi)	8m 1s
clang-valgrind-intltest (rbnf)	6m 28s
clang-valgrind-intltest (rbnfrt)	6m 14s
clang-valgrind-intltest (icuserv)	5m 33s
clang-valgrind-intltest (idna)	5m 55s
clang-valgrind-intltest (convert)	7m 5s
clang-valgrind-intltest (rbnfp)	6m 39s
clang-valgrind-intltest (csdet)	5m 37s
clang-valgrind-intltest (spoof)	5m 24s
clang-valgrind-intltest (bidi)	5m 54s
	2h 0m 10s

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