perf(ssr): calculate stacktrace offset lazily

[ohana54]

Description

I'm working on a cli which uses vite as a dependency.
I'm also using the source-map-support package to transform error stacktrace frames.

When running the cli, the vite module is loaded. During the load, it eagerly creates an Error and accesses its stack property, which triggers source mapping.
This is pretty slow and incurs a few hundred ms on my cli's startup time (might be different numbers on different hardware).

Proposed solution - calculate the offset (which accesses stack) lazily - only when we actually need to rewrite an ssr stacktrace.

Additional context

1. I didn't add a test that will break without this change, don't know if it's possible and/or worth it. Will be happy to add with some help.
2. I labeled the PR as a refactor, I didn't really know what is the category for that. Is this considered a perf improvement?

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[sapphi-red]

Thanks! LGTM