Added CTS and user identifiers features [ENT-22836]

[DorAshkenaziHuman]

https://perimeterx.atlassian.net/browse/ENT-22836

[Copilot]

Pull request overview

Adds support for extracting Cross-Tab Session (CTS) and JWT-based user identifiers and forwarding them to PerimeterX risk/activity payloads.

Changes:

• Introduces a JwtExtractor to pull app_user_id and optional additional fields from a JWT in a configured cookie or header.
• Extracts CTS from the pxcts cookie and includes CTS/JWT identifiers in Risk API and Activities payload “additional” fields.
• Updates docs/metadata to reflect the new “user_identifiers” feature and configuration options.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/UserIdentifiers/JwtExtractor.php	New helper to decode JWT payload and extract configured fields.
src/Perimeterx.php	Adds JWT config defaults and plugs JWT extraction into additional fields creation.
src/PerimeterxContext.php	Stores CTS/app user id/JWT additional fields on the request context.
src/PerimeterxS2SValidator.php	Adds CTS/JWT identifier fields to Risk API request body; includes decoded cookie for sensitive_route.
src/PerimeterxActivitiesClient.php	Adds CTS/JWT identifier fields to activity details payload.
src/PerimeterxRiskClient.php	Docblock update for millisecond timestamp return type.
src/PerimeterxLogger.php	Docblock update to allow Stringable messages.
px_metadata.json	Advertises user_identifiers capability.
examples/test-adapter.php	Adds config mapping support for JWT identifier options in spec tests.
README.md	Documents JWT User Identifiers feature and configuration options.
CHANGELOG.md	Adds changelog entry for CTS/JWT identifiers and sensitive-route decoded-cookie behavior.

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