Add checks for ascii digits in time decode functions #10365

Job	Run time
make check (--enable-asynccrypt --enable-all --enable-dtls13 CFLAGS="-pedantic -Wdeclaration-afte...	2m 54s
make check (--enable-ocsp CFLAGS="-DTEST_NONBLOCK_CERTS -pedantic -Wdeclaration-after-statement -...	1m 8s
make check (--enable-asynccrypt --enable-all --enable-dtls13 --disable-mlkem CFLAGS="-pedantic -W...	2m 51s
make check (--enable-asynccrypt-sw --enable-ocspstapling --enable-ocspstapling2 --disable-mlkem C...	1m 27s
make check (--enable-asynccrypt-sw --enable-ocspstapling --enable-ocspstapling2 CFLAGS="-pedantic...	1m 21s
	9m 41s

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