feat(unstable): implement custom inspect for Deno.AtomicOperation

[lswith]

Summary

Adds a custom inspect method to AtomicOperation to provide a readable string representation of the queued operations (checks, mutations, enqueues). This improves developer experience when debugging atomic operations by showing the internal state in a human-readable format.

The implementation adds a custom [Symbol.for("Deno.customInspect")] method that formats the operations into a structured string showing:

• Check operations with their keys and versionstamps
• Mutation operations (set, delete, sum) with keys and values
• Enqueue operations with payloads and options

Related Issues

Fixes #21034

The issue requested better debugging/logging support for the AtomicOperation class to help developers understand what operations are queued in an atomic transaction.

Changes

• Added [Symbol.for("Deno.customInspect")] method to AtomicOperation class
• Implemented formatting for check, mutation, and enqueue operations
• Added comprehensive test coverage in tests/unit/kv_test.ts

Testing

• Added comprehensive unit tests covering:
  • Empty atomic operations
  • Operations with checks only
  • Operations with mutations only (set, delete, sum)
  • Operations with enqueues only
  • Complex combinations of all operation types
  • Special value handling (Uint8Array, null, undefined, bigint)

All tests verify the expected human-readable inspection strings match the actual output from Deno.inspect().

Checklist

• ✅ Tests cover the changes
• ✅ cargo test passes
• ✅ ./tools/format.js passes without changing files
• ✅ ./tools/lint.js passes
• ✅ Referenced related issue Useful output when logging AtomicOperations #21034

Release Notes

### kv

- Added custom inspect for `AtomicOperation` to provide readable output for debugging atomic transactions.

[CLAassistant]

All committers have signed the CLA.

[lucacasonato]

LGTM, thanks!