Feat/currency placeholder and local caching

[TheBjoRedCraft]

No description provided.

[Copilot]

Copilot review overview

🔵 Needs a closer look

It adds concurrency-sensitive caching with cross-node Redis invalidation on the money/balance path, with no tests in the affected modules, so final human review is warranted.

Review effort: Balanced
Findings: None

What changed in this PR

This PR adds locally-cached, non-suspending balance reads for the client runtime and exposes them through PlaceholderAPI on Paper. A new BalanceCache keeps per-default-account balances in a Caffeine cache that is never recomputed locally; instead, whenever a transaction touches an account the balance is re-queried from the microservice. Cross-node consistency is achieved by publishing a BalanceChangedEvent over Redis so other servers refresh their cached entries, while the originating server refreshes locally and skips its own event. Three PAPI placeholders (current-balance, current-balance-short, currency-display) surface this data in-game.

Changes:

• Introduce BalanceCache (background-loaded, versioned, event-invalidated) and wire TransactionServiceImpl to invalidate it on every balance-changing operation (begin/commit/rollback/deposit/withdraw/transfer).
• Add BalanceChangedEvent + BalanceEventsListener and register the listener in RedisService; dispose the cache scope on client shutdown.
• Add PAPI placeholders and expansion, registered from PaperMain; bump Gradle wrapper to 9.8.0 and project version to 4.1.8.

File	Description
.../​balance/​BalanceCache.kt	New non-suspending balance cache with background loading, versioned refresh, and Redis-based invalidation.
.../​transaction/​TransactionServiceImpl.kt	Invalidates BalanceCache on all balance-changing results via per-result-type transactions extensions.
.../​redis/​events/​balance/​BalanceChangedEvent.kt	New serializable Redis event carrying affected account IDs and currency name.
.../​balance/​BalanceEventsListener.kt	Refreshes cached balances on remote BalanceChangedEvent, skipping self-originated events.
.../​redis/​RedisService.kt	Subscribes the new BalanceEventsListener.
.../​client/​ClientTransactionalInstance.kt	Disposes the BalanceCache scope on client disable.
.../​papi/​placeholder/​CurrentBalancePlaceholder.kt	PAPI placeholder returning the full-precision cached balance.
.../​papi/​placeholder/​CurrentBalanceShortPlaceholder.kt	PAPI placeholder returning the cached balance rounded to 2 decimals.
.../​papi/​placeholder/​CurrencyDisplayPlaceholder.kt	PAPI placeholder returning a currency symbol.
.../​papi/​PapiExpansion.kt	Aggregates the placeholders into a PAPI expansion.
.../​paper/​PaperMain.kt	Registers the PAPI expansion on enable.
gradle/​wrapper/​gradle-wrapper.properties, gradle.properties	Gradle wrapper 9.8.0 and project version 4.1.8 bumps.

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