ci: add explicit timeouts to workflow jobs

[s6pa1rta3n-lab]

Closes #252

Adds explicit, conservative job timeouts (timeout-minutes) to every GitHub Actions workflow job in the repository without altering triggers, permissions, action versions, or execution steps.

Summary of Changes

Workflow	Job	Timeout	Rationale
bindings-check.yml	check	30m	Retains ample headroom for cold Rust installation (cargo install stellar-cli --locked) and binding generation checks (~15 min typical run).
contract.yml	round-contract	15m	Generous headroom for cold Soroban / Rust compilation and contract unit test suites (~1-2 min typical run).
coverage.yml	coverage	10m	Sufficient headroom for pnpm dependency installation and TypeScript test coverage runs (~1 min typical run).
docs-links.yml	check-links	5m	Headroom for node script checking local markdown links (~15s typical run).

Acceptance Criteria Verification

• Finite timeouts: Every workflow job defines timeout-minutes.
• Cold build headroom: Contract (15m) and binding check (30m) jobs have plenty of room for cold toolchain downloads and compilations.
• Untouched surface: Steps, triggers, permissions, and action versions are completely unchanged.
• YAML Validity: All workflow files parse and validate cleanly.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC