refactor: use renderFunctionErrorPage from @netlify/dev-utils

[keanu-a]

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Summary

Fixes #EX-366

Replaced all usages of renderErrorTemplate with renderFunctionErrorPage from @netlify/dev-utils, and deleted render-error-template.ts since now unused.

Ref: https://github.com/netlify/primitives/blob/main/packages/dev-utils/src/lib/errors.ts

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📊 Benchmark results

Comparing with 91b6c55

• Dependency count: 1,076 (no change)
• Package size: 295 MB (no change)
• Number of ts-expect-error directives: 382 ⬇️ 0.79% decrease vs. 91b6c55