DEV: Add a way to observe stores

[thetarnav]

• Adds a dev-only ability to observe stores by adding a new $ON_UPDATE symbol.
• the dev APIs are bundled into a DEV object, as in the core module (not sure if it should be called STORE_DEV to avoid conflicts, but it's probably whatever)
• Some typings got cleaned up too (nothing in public APIs though)
• Added a jsdoc comment to unwrap because why not

Draft because I still want to confirm if this is enough, and maybe add some unit tests.

[coveralls]

Pull Request Test Coverage Report for Build 3385674394

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 13 of 14 (92.86%) changed or added relevant lines in 3 files are covered.
• 14 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 89.078%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/solid/store/src/store.ts	11	12	91.67%

Files with Coverage Reduction	New Missed Lines	%
packages/solid/store/src/store.ts	1	95.38%
packages/solid/src/render/component.ts	13	71.52%

Totals
Change from base Build 3287627654:	-0.01%
Covered Lines:	1284
Relevant Lines:	1371

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💛 - Coveralls

[thetarnav]

Alright, I think this one's ready
I've changed the API to use a global listener, similar to the existing afterUpdate and afterRootCreate hooks.
This will allow for more flexibility and storing updates without pre-patching anything.