feat(escrow_contract): implement escrow lifecycle for issues 7-10

[ALIPHATICHYD]

This PR implements the full escrow lifecycle in the escrow contract, including payment locking on creation, fee-aware release, full refunds, and dispute-triggered escrow pausing with dispute metadata.

What changed
Added robust escrow creation flow with sender auth, token transfer to contract, duplicate delivery rejection, Locked state, and created_at timestamp.
Added recipient/admin controlled escrow release with Locked-state checks, platform fee basis-points calculation, fee transfer to admin, net transfer to driver, and Released transition.
Added sender/admin controlled refund path from Locked or Paused states, full refund with no fee deduction, and Refunded transition.
Added dispute flow where sender or recipient can pause a Locked escrow, recording disputed_by and disputed_at metadata.
Updated shared escrow types and contract tests to validate the full lifecycle and access-control/state-machine constraints.
Validation
Ran formatting and full workspace tests successfully:
cargo fmt --all
cargo test

Closes #7
Closes #8
Closes #9
Closes #10

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