perf(runner): use mimalloc as the global allocator

memtrack runs as a subcommand of this binary, so the allocator set in its own
`main.rs` no longer applies to it. Set mimalloc on the runner binary instead,
which covers memtrack and the rest of the runner alike.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: moha-bekh

Cargo.lock

@@ -77,6 +77,7 @@ uuid = { version = "1.23.1", features = ["v4"] }
 which = "8.0.2"
 crc32fast = "1.5.0"
 samply = { path = "crates/samply-codspeed/samply" }
+mimalloc = "0.1"
 
 # Memory profiling (memtrack) and the capability handling around it are Linux-only.
 [target.'cfg(target_os = "linux")'.dependencies]

Cargo.toml

@@ -1,3 +1,6 @@
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
+
 use codspeed_runner::{clean_logger, cli};
 use console::style;
 use log::log_enabled;