chore(mobility_features): widen carp_serializable constraint to allow 3.x (6.2.0)

[Zeroupper]

Widens the carp_serializable constraint so mobility_features works with both 2.x and 3.x.

carp_serializable 3.0.0 is a breaking release (it replaces the built-in Uuid with the uuid package). Today mobility_features pins ^2.0.0, which blocks carp_context_package in carp.sensing-flutter from resolving.

Change

• carp_serializable: ^2.0.0 → '>=2.0.0 <4.0.0'
• version 6.1.0 → 6.2.0

A range rather than ^3.0.0 keeps existing 2.x consumers working, so this is non-breaking for downstream users.

No code changes needed

The only breaking change in 3.0.0 is Uuid().v1 (getter) → const Uuid().v4() (method). lib/ has no Uuid references, so this is a constraint-only bump.

Verification

• resolves carp_serializable 3.0.0
• flutter test: the 4 failing tests in mobility_features_test.dart fail identically on unmodified master (FormatException while parsing test data) — pre-existing and unrelated to this change.

This one is independent of the other repos and can be merged/published on its own.