Add custom error types for catchable ORM failures

[rsslldnphy]

Summary

• Adds an OrmError base class so consumers can catch any ORM-thrown error with instanceof.
• Adds NotFoundError (single-row op found 0 rows), TooManyRowsError (single-row op found >1), and CreateFailedError (createOne got 0 rows back) — all extend OrmError.
• Each carries modelName and operation; TooManyRowsError also exposes rowCount.
• Replaces the generic throw new Error(...) calls in findOne, updateOne, deleteOne, and createOne with the new typed errors. Messages are preserved, so existing rejects.toThrow("...") assertions still match.
• Other throw new Error sites (schema lookups, missing where clauses, connection-state checks, operator validation) were left as plain Error — they're programmer errors, not runtime conditions worth catching.

import { NotFoundError, TooManyRowsError, OrmError } from "@casekit/orm";

try {
    await db.findOne("user", { where: { id } });
} catch (e) {
    if (e instanceof NotFoundError) {
        // e.modelName, e.operation
    } else if (e instanceof OrmError) {
        // any ORM-thrown error
    }
}

Test plan

• pnpm typecheck clean
• All previously affected tests still pass (findOne, updateOne, deleteOne, createOne, middleware.where, findOne.select, findOne.where, findOne.includeManyToOne)
• Reviewer sanity-check that the chosen error names and field shapes are what you want exposed publicly

[github-actions]

Coverage Report

• orm-cli: 96.85%
• orm-migrate: 94.02%
• orm: 98.41%
• sql: 97.03%
• toolbox: 100%