introduce ReadonlyTag as a Tag that can only be used to read a service from requirements

[mikearnaldi]

Introduce ReadonlyTag as the covariant side of a tag, enables:

import type { Context } from "effect"
import { Effect } from "effect"

export class MyRequirement extends Effect.Service<MyRequirement>()(
  "MyRequirement",
  { succeed: () => 42 }
) {}

export class MyUseCase extends Effect.Service<MyUseCase>()("MyUseCase", {
  dependencies: [MyRequirement.Default],
  effect: Effect.gen(function* () {
    const requirement = yield* MyRequirement
    return Effect.fn("MyUseCase.execute")(function* () {
      return requirement()
    })
  })
}) {}

export function effectHandler<I, Args extends Array<any>, A, E, R>(
  service: Context.ReadonlyTag<I, (...args: Args) => Effect.Effect<A, E, R>>
) {
  return Effect.fn("effectHandler")(function* (...args: Args) {
    const execute = yield* service
    yield* execute(...args)
  })
}

export const program = effectHandler(MyUseCase)

Discord discussion: https://discord.com/channels/795981131316985866/795983589644304396/1400218469160714261

[changeset-bot]

🦋 Changeset detected

Latest commit: f65f14c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 35 packages

Name	Type
effect	Minor
@effect/cli	Major
@effect/cluster	Major
@effect/experimental	Major
@effect/opentelemetry	Major
@effect/platform-browser	Major
@effect/platform-bun	Major
@effect/platform-node-shared	Major
@effect/platform-node	Major
@effect/platform	Major
@effect/printer-ansi	Major
@effect/printer	Major
@effect/rpc	Major
@effect/sql-clickhouse	Major
@effect/sql-d1	Major
@effect/sql-drizzle	Major
@effect/sql-kysely	Major
@effect/sql-libsql	Major
@effect/sql-mssql	Major
@effect/sql-mysql2	Major
@effect/sql-pg	Major
@effect/sql-sqlite-bun	Major
@effect/sql-sqlite-do	Major
@effect/sql-sqlite-node	Major
@effect/sql-sqlite-react-native	Major
@effect/sql-sqlite-wasm	Major
@effect/sql	Major
@effect/typeclass	Major
@effect/vitest	Major
@effect/workflow	Major
@effect/ai	Major
@effect/ai-amazon-bedrock	Major
@effect/ai-anthropic	Major
@effect/ai-google	Major
@effect/ai-openai	Major

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