fix: handles integer foreign-key priority

[Zaimwa9]

Closes #214 , restoring previous behavior

• Fixes MismatchedInputException thrown by SDK 8.0.0–8.1.0 when deserializing /api/v1/identities/ responses from self-hosted Core/EE that include a flag with a segment override.

• Root cause: PR feat!: Context Values support, getEvaluationResult #184 dropped the FeatureSegmentModel(Integer) constructor that Jackson was using as a delegating creator to coerce Core/EE's integer FK shape (feature_segment: 321) into the model. Edge emits feature_segment: {"priority": <int>} and is unaffected.

• Restores the Integer-arg constructor (mirrors pre-feat!: Context Values support, getEvaluationResult #184 shape) so both wire formats deserialize correctly.

• SaaS / edge.api.flagsmith.com users were never affected.

• Core/EE wire-format inconsistency is the deeper issue and will be tracked separately — the SDK still needs this tolerance long-term to support older self-hosted installs.

  Test plan

• Added FeatureSegmentModelTest covering the three shapes: integer FK (Core/EE), engine object (Edge), and null (no segment override). Verified the integer-FK test fails on main with the reported exception, then passes after the fix.

  • Full unit test suite passes locally with no regressions.

[khvn26]

Fine, bar 1 comment.