Fix bugs, add missing test coverage, and clean up dead code in auto-exchange annotation framework

[Copilot]

Code review of the auto-exchange rate annotation across three dimensions: bugs, unit test coverage, and functional completeness.

Bug Fixes

Annotation processor source version mismatch — both processors declared @SupportedSourceVersion(RELEASE_11) on a Java 17 project, causing 2 test failures via compiler warning.

// Before
@SupportedSourceVersion(SourceVersion.RELEASE_11)
// After
@SupportedSourceVersion(SourceVersion.RELEASE_17)

ExchangeManager.init() NPE on null provider response — unlike refreshRates(), init() had no null guard on fetchData() return. Added consistent null check that retains cache on null response.

AutoExchangeContext used wrong map type — HashMap (equals/hashCode) was used to key per-bean appended data. Two distinct instances with equal hashCode/equals would collide. Changed to IdentityHashMap.

ExchangeBeanSerializerModifier.hasAutoExchangeFieldInHierarchy() was a stub — hardcoded return true wrapped every bean in AppendingBeanSerializer regardless of whether it had @AutoExchangeField. Replaced with real class hierarchy inspection backed by a ConcurrentHashMap cache.

Removed deprecated strategy classes with wrong hardcoded values — AppendApplyExchangeStrategy and InPlaceApplyExchangeStrategy had BigDecimal.valueOf(2) hardcoded as the exchange rate and "CNY" hardcoded as the target currency. Neither class was used. Removed along with AbstractApplyExchangeStrategyDeprecated.

Unit Tests Added

Previously untested paths now covered:

• ExchangeManagerTest — init() null handling, refreshRates() null retention, cache updates, rate not found
• AutoExchangeContextTest — identity-based key lookup, multiple fields per bean
• MissingRateThrowExceptionTest — THROW_EXCEPTION strategy returns HTTP 500 with structured error via AutoExchangeExceptionHandler (0% coverage before)
• MissingRateProtectiveTest — PROTECTIVE strategy applies configured protective rate
• MissingRateReturnNullTest — RETURN_NULL strategy yields null price field
• Added integration tests for HTTP header-based target currency, null @AutoExchangeField field values (should yield price=0, no NPE), and @AutoExchangeBaseCurrency runtime field resolution

Functional Completeness

• ApplyExchangeMode enum was defined but never referenced anywhere in the framework. Marked @Deprecated. (ICurrencyExchangeService and DefaultCurrencyExchangeService were already deprecated.)

Original prompt

这个自动应用汇率的注解，请审核下代码，从 bug，ut，功能完备性三个方面审查

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