feat: use sync.Pool to reduce alloc

[ethan256]

use sync.Pool to reduce alloc on conn.Receive.

[kung-foo]

Hi @ethan256, do you have some real-world motivation for wanting to introduce a pool?

[ethan256]

Hi @ethan256, do you have some real-world motivation for wanting to introduce a pool?
When I pressure tested it, I found that the program has a high GC percentage, and its pprof results are as follows:

Modified results：