Kitex v0.16.4 reports v0.16.3 #2008

The v0.16.4 release still defines kitex.Version as v0.16.3 in version.go, so its CLI reports the previous release:

$ go run ./tool/cmd/kitex --version
v0.16.3

Expected: v0.16.4, matching the release tag. The same constant remains on main.

Updating the constant to v0.16.4 corrects the output and lets Homebrew retain its version assertion alongside the functional code-generation test: Homebrew/homebrew-core#316931.