Remove all allocations in metrics system #20

Job	Run time
Check cargo fmt	37s
cargo check	3m 52s
build with wasm-pack	2m 23s
cargo test (macos)	3m 36s
cargo test (macos-aarch64)	3m 36s
Verify Vendored Code	50s
Verify MSRV (Min Supported Rust Version)	6m 30s
cargo test (win64)	7m 9s
clippy	0s
check Cargo.toml formatting	0s
cargo test hash collisions (amd64)	0s
check configs.md is up-to-date	0s
cargo doc	0s
cargo test (amd64)	0s
cargo test doc (amd64)	0s
cargo test datafusion-cli (amd64)	0s
cargo examples (amd64)	0s
Run sqllogictest with Postgres runner	0s
cargo test pyarrow (amd64)	0s
verify benchmark results (amd64)	0s
	28m 33s

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