fix(types): make request Refs covariant

[damusix]

Typed routes, lifecycle methods, pres, failActions, and extensions currently error whenever their Refs are not 100% identical — the limitation documented in test/types/index.ts ("Request not assignable to Request"). Three compounding causes:

1. Request embeds Lifecycle.Method<Refs> through route.settings, whose contravariant request parameter makes Refs effectively invariant — even plain widening (Request<{Payload: X}> → Request) fails.
2. Two contravariant keyof positions (paramsArray, pre assign) additionally block covariance. paramsArray was also mistyped: it holds the param values in path order, so it is string[].
3. TypeScript relates Request<A> to Request<B> by comparing the type arguments directly, and a partial Refs object can never satisfy the full ReqRefDefaults interface. The type parameter therefore now defaults to {} — reads are unchanged, since MergeRefs<{}> resolves to the same defaults.

The fix: Lifecycle.Method is declared through a method signature so comparisons are bivariant (the same technique React's typings use for event handlers), Request/ResponseToolkit are annotated out with the {} default, and the two keyof positions are made covariant-safe (assign keeps declared-key autocomplete via Extract<keyof ...> | (string & {})).

Net effect: a method typed with narrower refs attaches to any surface typed with the defaults (server.ext(), route ext, failAction, pre on untyped routes), and a route typed with a superset of refs accepts methods typed with any subset — while contradictory refs and default-to-narrow flows still error. Types-only; no runtime change.