Add unit tests for httpfsgateway, insight, and managed-rocksdb modules

[devin-ai-integration]

What changes were proposed in this pull request?

Add 104 unit tests across the three modules with the lowest test-to-source ratio in the repository:

Module	Before (test/source ratio)	Tests added
hadoop-ozone/httpfsgateway	1.58% (1 test / 63 source)	+64 tests (3 new test classes)
hadoop-ozone/insight	13.79% (4 tests / 29 source)	+36 tests (3 new test classes)
hadoop-hdds/managed-rocksdb	6.25% (2 tests / 32 source)	+4 tests (1 new test class)

httpfsgateway tests:

• TestParams (44 tests): covers the Param hierarchy — BooleanParam, IntegerParam, LongParam, ShortParam, EnumParam, EnumSetParam, StringParam (parsing, defaults, validation, domains) and the Parameters container (get, getValues, missing keys).
• TestCheckUploadContentTypeFilter (10 tests): exercises doFilter for GET/DELETE/PUT/POST with correct and incorrect content types for CREATE/APPEND upload operations.
• TestHttpFSExceptionProvider (10 tests): verifies exception-to-HTTP-status mapping (SecurityException → 401, FileNotFoundException → 404, IOException → 500, UnsupportedOperationException/IllegalArgumentException → 400), FileSystemAccessException unwrapping, and getOneLineMessage truncation.

insight tests:

• TestComponent (16 tests): constructors, equals/hashCode, prefix() formatting, and Type enum coverage.
• TestMetricDisplayClasses (9 tests): MetricDisplay, MetricGroupDisplay, and LoggerSource construction and accessors.
• TestNodeManagerInsight (11 tests): loggers, metrics groups, verbose/non-verbose level selection, and filterLog with various filter combinations.

managed-rocksdb tests:

• TestRocksDatabaseException (4 tests): verifies constructors and message formatting for both generic and RocksDBException causes.

What is the link to the Apache JIRA

N/A — test-only change to improve unit test coverage.

How was this patch tested?

All 104 new tests run and pass:

mvn -pl :ozone-httpfsgateway test → 64 tests, 0 failures
mvn -pl :ozone-insight test       → 36 tests, 0 failures
mvn -pl :hdds-managed-rocksdb test →  4 tests, 0 failures

Checkstyle (checkstyle:check) and RAT (apache-rat-plugin:check) pass with 0 violations across all three modules.

Generated-by: Devin (Claude)

Link to Devin session: https://app.devin.ai/sessions/e89718663af44b7aabfb200565fc6146
Requested by: @marcuslin123

[devin-ai-integration]

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