Migrate to Vitest v4

[molefrog]

• Removed Rollup bundler - no longer needed since the esm output is the same as the source and we don't need to build cjs anymore
• Migrated to Vitest v4 - updated from v3 to v4, fixed act() warnings in tests
• Fixed broken coverage reporting

[bolt-new-by-stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[github-actions]

size-limit report 📦

Path	Size
packages/wouter/esm/index.js	0 B (-100% 🔽)
packages/wouter/esm/use-browser-location.js	0 B (-100% 🔽)
packages/wouter/esm/memory-location.js	0 B (-100% 🔽)
packages/wouter/esm/use-hash-location.js	0 B (-100% 🔽)
packages/wouter-preact/esm/index.js	0 B (-100% 🔽)
packages/wouter-preact/esm/use-browser-location.js	0 B (-100% 🔽)
packages/wouter-preact/esm/use-hash-location.js	0 B (-100% 🔽)
packages/wouter-preact/esm/memory-location.js	0 B (-100% 🔽)
packages/wouter/src/index.js	2.19 KB (+100% 🔺)
packages/wouter/src/use-browser-location.js	526 B (+100% 🔺)
packages/wouter/src/memory-location.js	799 B (+100% 🔺)
packages/wouter/src/use-hash-location.js	732 B (+100% 🔺)
packages/wouter-preact/src/index.js	2.08 KB (+100% 🔺)
packages/wouter-preact/src/use-browser-location.js	456 B (+100% 🔺)
packages/wouter-preact/src/use-hash-location.js	660 B (+100% 🔺)
packages/wouter-preact/src/memory-location.js	721 B (+100% 🔺)

[molefrog]

Closing in favour of #546