elelem v0.1.0 — provider-neutral Go engine for LLM requests

First standalone release, extracted from the project it grew up in as an
internal package.

The engine is provider-neutral; the drivers are not. Application code holds
Driver, Client and Request, and the OpenAI and Anthropic SDK types never leave
their own packages. The conformance suite both shipped drivers run is part of
the public surface, so a third driver gets the same contract checked.

Covers streamed requests, a tool loop with bounded concurrency and per-tool
timeouts (manual by default, automatic via WithAutoToolCalls), history limiting
that treats an assistant tool call and its results as one indivisible unit,
retries that stop the moment output begins, usage accounting that separates
context from billed cost, and structured output validated against a schema
derived from the caller's own type.

Deliberately absent: storage, credential resolution, tool authorization,
presentation, and any kind of agent framework.