[Test] Add unit tests for StoreType.fromString tolerant parsing contract

Description

store/src/main/java/org/apache/rocketmq/store/StoreType.java's tolerant parsing has no direct unit test:

public static Set<StoreType> fromString(String str) {
    if (str == null || str.trim().isEmpty()) {
        return Collections.emptySet();
    }
    return Arrays.stream(str.split(";"))
        .map(String::trim)
        .filter(s -> !s.isEmpty())
        .map(s -> Arrays.stream(StoreType.values())
            .filter(type -> type.getStoreType().equalsIgnoreCase(s))
            .findFirst()
            .orElse(null))
        .filter(Objects::nonNull)
        .collect(Collectors.toSet());
}

fromString is the parsing path behind the storeType broker configuration (used by CombineConsumeQueueStore to select the consume-queue implementation), and its behavior is full of deliberate edge cases that nothing currently pins down:

• null / empty string / all-whitespace input → empty set
• case-insensitive matching (DEFAULT, default, DefaultRocksDB, ...)
• surrounding whitespace trimmed per segment
• empty segments between semicolons skipped ("default;;rocksdb")
• duplicate entries deduplicated by the returned Set
• unknown tokens silently dropped ("default;unknown" → {default})

There is no StoreTypeTest in the repo, and no existing test calls fromString directly. A future refactor of this method (e.g. switching to an enum valueOf or changing separator handling) would silently change broker store-type parsing with no failing test.

Expected behavior

Add a StoreTypeTest covering the behaviors above so the parsing contract is locked (e.g. " default ; DEFAULTROCKSDB;default;unknown;; " → {DEFAULT, DEFAULTROCKSDB}).