feat: Add optional context to migrations

[FoxxMD]

• Implements an optional, typed second argument to up/down that is passed through apply/rollback
• Allows users to provide their own context for migration code
• Update docs to provide context example

Closes #2

Should remain backwards compatible. Here is the added docs example that provides an example of how this would be used:

---

A second argument can be provided to migration file functions in order to supply your own context. Context should be passed in apply or rollback.

To enforce type correctness, type the Migrator and use satisfies in your migration files:

import type { SqliteDatabase, Migration } from 'sqlite-up';

interface MyContext = {
  foo: string
}

export const up: Migration<MyContext>['up'] = async (db: SqliteDatabase, ctx: MyContext): Promise<void> => {
  // Migration code here
  // context is passed as ctx
};

export const down: Migration<MyContext>['down'] = async (db: SqliteDatabase, ctx: MyContext): Promise<void> => {
  // Rollback code here
  // context is passed as ctx
};

Later, when using the migrator...

import { DatabaseSync } from 'node:sqlite';
import { Migrator } from 'sqlite-up';

async function main() {
  const db = new DatabaseSync('myapp.db');

  const migrator = new Migrator<MyContext>({
    db,
    migrationsDir: './migrations',
  });

  const result = await migrator.apply({foo: 'bar'});
}

main().catch(console.error);

[sandrinodm]

Very useful, thanks @FoxxMD!