feat: add elicit_* newtype crates for csv, bincode, and nom error types

[crumplecup]

Summary

Following the pattern established by elicit_uuid, we need newtype wrapper crates for error types from csv, bincode, and nom so that structs containing these errors can fully derive Elicit. This would enable agent-generated mocks for error-path testing.

Context

In the destination library we have the following error types that currently cannot derive Elicit:

Error struct	Blocking field type	Crate
Io	std::io::Error	std
Csv	csv::Error	csv
Decode	bincode::error::DecodeError	bincode
Encode	bincode::error::EncodeError	bincode
Nom	nom::Err<nom::error::Error<String>>	nom

std::io::Error already has an Elicitation impl in primitives/errors.rs (using the Generator pattern), but is missing a JsonSchema impl, so the derive still fails.

csv::Error, bincode::error::DecodeError/EncodeError, and nom::Err are missing both an Elicitation impl and a JsonSchema impl.

Proposed solution

Add newtype wrapper crates following the elicit_uuid pattern:

• elicit_io (or extend elicitation core) — newtype for std::io::Error with JsonSchema + Elicitation. The Generator pattern already exists in primitives/errors.rs; this just needs a JsonSchema impl and a newtype wrapper.
• elicit_csv — newtype for csv::Error with Generator-based Elicitation + JsonSchema
• elicit_bincode — newtypes for bincode::error::DecodeError and bincode::error::EncodeError
• elicit_nom — newtype for nom::Err<nom::error::Error<String>>

Each newtype should:

1. Derive or implement JsonSchema (likely as { "type": "string" } with a descriptive title, since these are opaque error types)
2. Implement Elicitation using the Generator pattern (enumerate error modes, construct the error from the selected mode)
3. Implement Deref/DerefMut and From/Into for transparent use as drop-in field replacements
4. Implement Display, Debug, std::error::Error forwarding

Acceptance criteria

With these crates in place, the following should compile and work end-to-end in destination:

#[derive(Debug, JsonSchema, Elicit)]
pub struct Io {
    path: std::path::PathBuf,
    source: elicit_io::IoError,  // or similar
    line: u32,
    file: String,
}

Notes

• std::io::Error is the highest priority since the Elicitation impl already exists — it just needs a JsonSchema wrapper and newtype.
• The nom error type is generic (nom::Err<nom::error::Error<String>>) — the newtype may need to fix the inner type to String to keep the schema concrete.
• All four cases use error types that cannot be meaningfully round-tripped through JSON; the Generator/mode enum pattern (as used for io::Error today) is the right approach for all of them.