Modernize ResourceT v2 with cancellation safety and structured concurrency

[robertdp]

Summary

This prepares ResourceT 2.0 for PureScript 0.15.16 and Spago 1.0.4 while closing resource-ownership and cancellation gaps. Managed forks now use structured concurrency: a resource scope owns, awaits, and cancels its child fibers.

Key changes

• replace the legacy Bower/Dhall setup with spago.yaml, registry package set 80.8.1, strict and pedantic builds, and committed lockfiles;
• make allocate cancellation-safe across acquisition and registry insertion, while retaining acquire as an alias;
• bind opaque release keys to their originating registry and provide atomic release and unprotect operations;
• run remaining finalizers once in LIFO order and aggregate reportable body, child, and cleanup failures;
• add nursery-backed scopes so managed children finish before parent resources are released;
• rebuild Control.Monad.Resource.Aff.Pool on the nursery;
• require Node.js 24 or newer for the repository toolchain;
• update CI, package metadata, formatting, and the BSD-3-Clause license.

Consumer documentation

• rewrite the README as the package overview and quick start;
• add a focused guide for allocation, release keys, ownership transfer, managed children, error behavior, transformer stacks, and the compatibility pool;
• expand generated API documentation at the public module boundary;
• compile-check representative documentation examples in test/Docs.purs;
• remove the changelog and migration material.

Important behavior

• Control.Monad.Resource.fork and forkAff create managed children. Scope exit waits for them, and a failed or directly cancelled child fails the scope and cancels managed siblings.
• Intentionally detached work uses Effect.Aff.forkAff directly and must not retain scoped resources.
• allocate is the canonical acquisition API; acquire remains an alias.
• Release keys are registry capabilities and cannot affect another scope.
• External fiber cancellation attempts cleanup but suppresses cleanup errors because Aff has no error-return channel for finalizer failures on that path.

Validation

Run under Node.js 24.20.0:

• npm ci
• npm run format:check
• npm test — 12/12 tests passed; strict/pedantic build produced no warnings or errors
• npm run docs — documentation generated successfully
• documentation examples compiled through the test build
• relative documentation links and stale references checked
• independent lifecycle and consumer-documentation reviews found no blocking or major issues

Spago's documentation search-index step emits non-fatal warnings for dependency purs.json metadata. The npm development toolchain reports seven inherited advisories; this package has no runtime npm dependencies.