Apply cargo clippy suggestions to reduce not needed allocations

[MTRNord]

Hi,

I applied the non style related clippy suggestions. (apart from the map_clone one and single_match in some places)

Namely:

• https://rust-lang.github.io/rust-clippy/master/index.html#single_match
• https://rust-lang.github.io/rust-clippy/master/index.html#explicit_counter_loop
• https://rust-lang.github.io/rust-clippy/master/index.html#redundant_closure
• https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone (coming from to_string)
• https://rust-lang.github.io/rust-clippy/master/index.html#map_clone

I also removed some calls to format! which should be not needed and allocate a String while not needed. (Though I am not sure if napi will do this anyway for FFI)

Signed-off-by: Marcel Radzio support@nordgedanken.dev