stupidgcm: batch C calls in chacha20poly1305_seal

Go has a high overhead for each C call, so batch
all openssl operations in the new C function chacha20poly1305_seal.

Benchmark results:

internal/speed$ go test -bench BenchmarkStupidXchacha -count 10 > old.txt
internal/speed$ go test -bench BenchmarkStupidXchacha -count 10 > new.txt

internal/speed$ benchstat old.txt new.txt
name             old time/op   new time/op   delta
StupidXchacha-4   8.79µs ± 1%   7.25µs ± 1%  -17.54%  (p=0.000 n=10+10)

name             old speed     new speed     delta
StupidXchacha-4  466MB/s ± 1%  565MB/s ± 1%  +21.27%  (p=0.000 n=10+10)

0 files changed, 0 insertions, 0 deletions