fix: Fix panic during CSV import when encountering invalid floats

[moore-ryan]

This fix will address #432, which was caused by an unchecked unwrap() after trying to convert a F64 value to a JSON Number. Since JSON Numbers cannot wrap NaN or Inf values, this would previously fail if encountering a string of the form "Nan" or "Inf"

Additionally, this change bumps up the version of the log dependency in synth/Cargo.toml from 0.4.11 to 0.4.18 to fix a compilation issue on recent nightly toolchains (see this issue in async-std for more info)

[moore-ryan]

Ah, I had run clippy, but did not fix up the warning because it was in existing code. Just pushed a changeset after running cargo fmt and cargo clippy (had to add an #[allow for clippy to pass, there was an existing unit test that was using a default unit struct).