fix: move amET locale to ethiopic package

[gpbl]

What Changed

Moves the amET locale implementation into @daypicker/ethiopic and removes the amET export from the main react-day-picker/locale barrel.

Also updates the v10 Ethiopic docs and upgrading guide to point amET consumers to @daypicker/ethiopic, adds a package entry-point test for the locale export, and includes a changeset for react-day-picker and @daypicker/ethiopic.

Review Notes

This keeps the Ethiopic-specific locale owned by the Ethiopic calendar package while leaving the generic shared locale re-exports alone.

Validation run locally:

• pnpm exec jest --selectProjects packages packages/ethiopic/src/locale/am-ET.test.ts packages/ethiopic/src/index.test.ts packages/ethiopic/src/ethiopic/index.test.tsx
• pnpm --filter react-day-picker run build
• pnpm --filter @daypicker/ethiopic run build
• pnpm --filter website run typecheck
• pnpm --filter website run build
• pnpm lint
• pnpm typecheck

[changeset-bot]

🦋 Changeset detected

Latest commit: ec25c63

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@daypicker/ethiopic	Patch
react-day-picker	Patch
@daypicker/buddhist	Patch
@daypicker/hebrew	Patch
@daypicker/hijri	Patch
@daypicker/persian	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR