fix(js-sdk): preserve multi-source COPY in fromDockerfile

[serejaris]

Summary

• Fixes Template().fromDockerfile() dropping all but the first source in multi-source Dockerfile COPY instructions.
• Emits one template COPY step per source while preserving the shared destination and COPY flags like --chown.
• Adds regression coverage for multi-source COPY and a patch changeset for the JS SDK.

Fixes #1349

Test plan

• pnpm --filter e2b exec vitest run tests/template/methods/fromDockerfile.test.ts -t "multi-source COPY"
• pnpm --filter e2b exec vitest run tests/template/methods/fromDockerfile.test.ts
• pnpm --filter e2b run typecheck
• pnpm --filter e2b run lint
• pnpm --filter e2b run build
• pnpm --filter e2b exec prettier --check src/template/dockerfileParser.ts tests/template/methods/fromDockerfile.test.ts

[cla-bot]

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[changeset-bot]

🦋 Changeset detected

Latest commit: fdf1d17

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

This PR includes changesets to release 1 package

Name	Type
e2b	Patch

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[serejaris]

Closing this as superseded by #1355.\n\nI compared the two PRs: this branch only covers the JS path and is still CLA-blocked, while #1355 covers both JS and Python , includes the multi-source COPY/ADD regressions in both SDKs, and has the maintainer-owned checks/CLA path.\n\nThanks for picking this up; I will track #1355 instead.

[serejaris]

Small correction to the comparison above: this branch covers the JS Template.fromDockerfile path, while #1355 covers both JS Template.fromDockerfile and Python Template.from_dockerfile.