fix: add back Optional type import

[zkhalapyan]

#138 removed the inclusive import of ./shared preventing Optional from getting imported properly, breaking external builds. See issue: metaplex-foundation/js#139.

PR converges all types under types.ts and directly imports Optional.

Tested that external builds work by manually importing the local forked npm package via npm link and building using tsc.

fixes #139

[aheckmann]

locally tested against wonka to confirm the fix. landing this, thanks!

will handle creating a reproducible test scenario for this separately so we avoid this in the future.

[zaxozhu]

🎉 This PR is included in version 4.11.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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