Remove User Id header

[stevensJourney]

Overview

This removes an unnecessary User-Id header which is currently being added to PowerSync service requests.

This header has not been used by the service for a long time.

The parameter in PowerSyncCredentials has been deprecated.

[Copilot]

Pull Request Overview

This pull request removes the obsolete "User-Id" header from internal PowerSync service requests and deprecates the associated property in the credentials class. Key changes include:

• Removing the "User-Id" header addition in SyncStream.
• Deprecating the userId property in PowerSyncCredentials.
• Updating the CHANGELOG and README to reflect the removal.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
core/src/commonMain/kotlin/com/powersync/sync/SyncStream.kt	Removed the unused "User-Id" header from HTTP header configuration.
core/src/commonMain/kotlin/com/powersync/connectors/PowerSyncCredentials.kt	Deprecated the userId property and maintained its inclusion in toString output.
README.md	Adjusted documentation to match new header configuration.
CHANGELOG.md	Updated changelog to document the removal of the "User-Id" header.

Comments suppressed due to low confidence (1)

core/src/commonMain/kotlin/com/powersync/connectors/PowerSyncCredentials.kt:30

• The deprecated userId property is still included in the toString output, which may lead to confusion on its usage. Consider updating this method to remove or adjust the representation of userId.

override fun toString(): String = "PowerSyncCredentials<endpoint: $endpoint userId: $userId>"