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feat(signals,solid): seedless derived stores; seeds are a complete T again (#4073)

createStore(fn), createProjection(fn) and createOptimisticStore(fn) accept a
derive that takes no draft and answers a complete value (sync, promise, or an
async iterable of complete snapshots). Plain-object roots only; arrays keep
their `[]` seed. The root starts as an empty record, an unobservable draft
like any seed (A25, D-30), so hydration replay and the setter's draft work as
they do with a `{}` seed today. `seedLoadingValue` is not offered without a
seed. Pass `undefined` for the seed to reach the options.

With the seedless form in place, a seed is a complete T again: the reason
#3258 was reverted (async stores that need the options slot had to invent a
T) is covered by `createStore(fn, undefined, options)`.

Types from Gabriel's #3194 exploration (NoArray, the return-only overload).



Claude-Session: https://claude.ai/code/session_01JJ7QVVnmnQrdvYP548mWWc

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Gabriel Valfridsson <gabriel.valfridsson@gmail.com>

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