Avoid per-write virtual dispatch in `DictionaryValuesWriter.shouldFallBack()` by caching the size-exceeded check

从 DictionaryValuesWriter.shouldFallBack() 和 FallbackValuesWriter.checkFallback() 开始，然后检查 Binary、Long、Double、Integer 和 Float 这些类型化子类的 write 方法，尤其是它们的 id == -1 分支。确认只有在添加新的字典条目时才会更新超出大小限制的状态，并且对于重复写入，fallback 行为保持不变。

Describe the enhancement requested

DictionaryValuesWriter.shouldFallBack() is called by FallbackValuesWriter.checkFallback() after every single value write. The current implementation dispatches a virtual call to getDictionarySize() on every invocation:

public boolean shouldFallBack() {
  return dictionaryByteSize > maxDictionaryByteSize || getDictionarySize() > MAX_DICTIONARY_ENTRIES;
}

getDictionarySize() is an abstract method overridden in each typed subclass (Binary, Long, Double, Integer, Float) to return the backing map's .size(). Since shouldFallBack() is polled after every write, including writes of duplicate values that do not grow the dictionary, the virtual dispatch and map-size query are redundant work for the common case where most values are already in the dictionary.
Both dictionaryByteSize and the dictionary entry count can only increase when a new entry is added (inside the if (id == -1) branch of each subclass's write method). Therefore the size-exceeded condition can only transition from false to true at that exact point.

Proposal

Replace the per-write check with a cached boolean dictionarySizeExceeded flag. Introduce a checkDictionarySizeLimit(int newDictionarySize) method that subclass write methods call only when a new dictionary entry is actually added. shouldFallBack() then returns the cached flag directly, a simple field read with no virtual dispatch.

Component(s)

Core