feat(escrow): introduce typed contracterror codes

[Edoscoba]

summary

Adds a typed EscrowError #[contracterror] enum for LiquiFact escrow failures, replacing ad-hoc string assert! / panic! paths with stable numeric contract error codes clients can branch on.

Changes include:

• Converted funding, settlement, withdrawal, claim, init, dust sweep, attestation, refund, admin, cap, and token-transfer failures to typed errors.
• Added exact try_* tests for representative ContractError(code) paths.
• Updated docs/escrow-error-messages.md with the canonical append-only error code table.
• Preserved auth boundaries, checked arithmetic, refund double-spend protection, claim idempotency, and token balance-delta safety checks.

Validation:

• cargo fmt -p liquifact_escrow -- --check
• cargo clippy -p liquifact_escrow -- -D warnings
• cargo test: 371 passed; 0 failed; 14 ignored
• cargo build --target wasm32v1-none --release -p liquifact_escrow
• Coverage: 96.43% line coverage with cargo llvm-cov

close #252

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