fix: disable lazy hydration when not using lazy-loading to avoid binary-size cost

[gbj]

#3988 (included in 0.8.5) introduced support for async hydration to support hydrating routes that included lazy-loaded WASM. However, this accidentally meant duplicating the hydration code for all AnyView types, which bloats the WASM binary size for all applications, including those not using lazy-loading.

This can be resolved by:

1. removing hydrate_async for applications that don't activate a lazy feature
2. and even better, removing hydrate for applications that do use it

However, requiring a lazy feature is a breaking change. In the meantime, I'd encourage people to try out this PR as a smallish patch, to see if it resolves the binary-size increase.