[ANCHOR-1154] Validate SEP-38 quote expiration

[philipliu]

Description

Validate that the SEP-38 quote expires in SEP-6/24/31 request handlers.

Context

The endpoints should not accept expired quotes by default but validating the expiration at this stage is not enough because the quote can expire when the funds arrive. This is more of a hardening fix.

Testing

• ./gradlew test

Documentation

N/A

Known limitations

N/A

[Copilot]

Pull request overview

Adds server-side hardening to reject expired SEP-38 quotes during request handling for SEP-6/24/31 flows by introducing consistent, injectable time sources and enforcing expires_at checks where quotes are validated/consumed.

Changes:

• Introduce a shared UTC Clock bean and inject it into SEP wiring and time-dependent components.
• Enforce quote-expiration validation in ExchangeAmountsCalculator (affecting SEP-6/24 quote usage) and in Sep31Service quote pre-validation.
• Update and extend unit tests to cover expired-quote scenarios and constructor signature changes.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
platform/src/main/java/org/stellar/anchor/platform/component/sep/SepBeans.java	Adds a UTC Clock bean and wires it into NonceManager, ExchangeAmountsCalculator, and Sep31Service.
core/src/main/java/org/stellar/anchor/util/ExchangeAmountsCalculator.java	Validates quote.expiresAt against an injected Clock when validating quotes for SEP-6/24.
core/src/main/java/org/stellar/anchor/sep31/Sep31Service.java	Rejects expired quotes during SEP-31 postTransaction pre-validation using an injected Clock.
core/src/test/kotlin/org/stellar/anchor/util/ExchangeAmountsCalculatorTest.kt	Updates constructor usage and adds a test to ensure expired quotes are rejected.
core/src/test/kotlin/org/stellar/anchor/sep31/Sep31ServiceTest.kt	Updates constructor usage and adds coverage for expired quote_id.
core/src/test/kotlin/org/stellar/anchor/sep24/Sep24ServiceTest.kt	Updates ExchangeAmountsCalculator construction to include Clock.
core/src/test/kotlin/org/stellar/anchor/util/ClientFinderTest.kt	Removes cross-test coupling by using the local token reference.

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