Log a warning when `path` is supplied on HASH storage

[banker]

IndexSchema.makeField currently has a silent TODO:

// src/schema/schema.ts:206
} else {
    // For HASH storage, path should always be null
    if (path !== null && path !== undefined) {
        // TODO: log a warning
    }
    field.path = null;
}

Users who set a JSON path on a HASH-storage field get their value silently dropped. A warning would surface the misconfiguration.

Acceptance criteria

• Warn (via console.warn or a logger if one is introduced) when a non-empty path is supplied for a HASH-storage field.
• Include the field name and the storage type in the warning.
• Unit test covering the warning surface.