ci: fix large enum and error types to clippy recommended sizes

[notmandatory]

This was flagged after updating the CI stable rustc to 1.87.0, See #242. Fix below to fit in clippy recommended sizes and then remove exceptions in clippy.toml.

• enum-variant-size-threshold, see: https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant

• large-error-threshold, see: https://rust-lang.github.io/rust-clippy/master/index.html#result_large_err