perf: cache dynamic imports of nodes

[gtm-nayan]

Dunno why but node spends a lot of time in esm loader land even for modules that have already been imported. This PR makes it so that the dynamic imports are only called once and that value is cached for any future calls. This increases rps by a little over 1.5x on my machine.

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[Rich-Harris]

Is there any reason we wouldn't always cache loaders? There's no danger of a memory leak since you can't clear the module cache anyway

[gtm-nayan]

I was thinking of dev mode and hosts which would create a new environment for each request.

[benmccann]

I was curious based off your comments on Discord, would we implement this differently if we could make breaking changes? just wondering if we should add a TODO for kit v2?

[gtm-nayan]

Maybe? Not necessarily Kit v2 but it'd be a breaking change for adapters.

I was thinking of adding something like injectImport to builder.generateManifest params and then using that to pull the __memo function from @sveltejs/kit/private-utils, same for all the component wrappers.

But thinking about it more, that isn't much cleaner so I'd likely leave it as is. Unless a better solution comes along.

[gtm-nayan]

Ugh, the lint, I should really stop using Github for edits lol. Thanks.