Add signals implementation

[silesky]

Add signals implementation.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 1ba9c94e6b85f11bb4e2bcca8018897cef20329d

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

This PR includes changesets to release 3 packages

| Name | Type | | -------------------------- | ----- | | @segment/analytics-next | Minor | | @segment/analytics-signals | Patch | | @internal/signals-example | Patch |

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