Add jemalloc for better memory management

[twdamhore]

Summary

Fixes memory not being returned to OS after serving large files.

Root cause: glibc's default allocator keeps freed memory for potential reuse instead of returning it to the OS.

Fix: Use jemalloc which has better memory return behavior.

Changes

• Added tikv-jemallocator dependency
• Set jemalloc as global allocator in main.rs

Test plan

# Build and install
cargo build --release
sudo cp target/release/serabutd /usr/local/bin/
sudo systemctl restart serabutd

# Serve a large file, then check memory after transfer completes
watch -n1 'ps -o rss= -p $(pgrep serabutd)'

Memory should drop back down after file transfer completes.

🤖 Generated with Claude Code