WIP: Refactor client to support custom connections

[slvrtrn]

Summary

Refactor the client to support custom connections.

NB: I haven't implemented connections other than the existing Node.js one yet; the first attempt (browser) is planned as a follow-up. This is just the necessary restructuring before we can make some progress there.

Related issues:

• Remove platform-specific dependencies #162
• Support for environments without access to http #153

The code now is a small monorepo, divided into several workspaces

• common (platform-independent types, data/query formatting, and other utils)
• client (the main client with all the config parsing and validation, without the connection layer, depends on the common workspace)
• node connection (the actual Node.js implementation, which depends on the client workspace)

The idea is that we can create new connections (fetch/axios/whatever) as just a new workspace and run CI using all of them one by one (run all tests with node connections, run a subset of tests for the browser, etc).

This also means we will have multiple NPM packages - the base client itself without a connection implementation included (replacing current @clickhouse/client) and at least one package per connection (@clickhouse/client-node, @clickhouse/client-fetch). The end user will have to install only one, though. This PR does not address the release routine (need to address the imports/paths, adjust GitHub Actions, etc)

Once it is released (when at least one new connection is made), the changes for the existing Node.js users should be minimal, just a simple change of import (createClient will come from @clickhouse/client-node instead of @clickhouse/client).

For example, with @clickhouse/client-node:

import { createClient } from '@clickhouse/client-node'
const client = createClient({
  host: getFromEnv('CLICKHOUSE_HOST'),
  password: getFromEnv('CLICKHOUSE_PASSWORD'),
})

See the workspace source for more details.

However, if just @clickhouse/client is added as a dependency, it is now possible to implement a custom version of the Connection interface and pass it with client configuration options.

For example:

const client = new ClickHouseClient({
  host: 'http://<host>:<port>',
  connection: (config) => new MyCustomConnection(config),
})

Where MyCustomConnection implements

export interface Connection {
  ping(): Promise<boolean>
  close(): Promise<void>
  query(params: BaseQueryParams): Promise<QueryResult>
  exec(params: BaseQueryParams): Promise<QueryResult>
  insert(params: InsertParams): Promise<InsertResult>
}

See connection.ts for more details.

Currently, we have stream and Buffer as leftover Node.js-specific types in the common module. However, there are polyfills available:

• Streams: https://www.npmjs.com/package/web-streams-polyfill
• Buffer: https://www.npmjs.com/package/buffer

Again, as a follow-up, I will investigate what is possible for the browser or, for example, Cloudflare workers since these are the common use cases.

Checklist

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[slvrtrn]

Changed the base branch from main to 0.1.0 cause I expect that it will take several PRs before we have it ready.

[slvrtrn]

Closing this in favor of #165