Use VecDeque for storing entry indexes in log batch

[tabokie]

After rust-lang/rust#88717, append is favored over extend-ing a Vec. This PR updates toolchain and change all entry indexes containers to VecDeque.

Micro-benchmark shows 6% improvements when appending 10 indexes:

vec:
test memtable::tests::bench_memtable_append                 ... bench:         350 ns/iter (+/- 67)
test memtable::tests::bench_memtable_append                 ... bench:         347 ns/iter (+/- 21)
vecdeque:
test memtable::tests::bench_memtable_append                 ... bench:         328 ns/iter (+/- 49)
test memtable::tests::bench_memtable_append                 ... bench:         326 ns/iter (+/- 36)