feat(import): add support for multiple hbase snapshot imports

[tianlei2]

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b/429250716

This is the first PR that incorporates changes from https://github.com/jhambleton/java-bigtable-hbase/commits/dataflow-v2-v2.15.6 and some fixes to make it pass the tests.

• Fixed Test Isolation Issues
  SnapshotUtilsTest.testGetHbaseConfiguration was failing because the static configuration field SnapshotUtils.hbaseConfiguration cached state between test cases, leaking stale data into subsequent tests.
  Solution: Added a @before setup method to reset the static field to null via reflection before every test run.
• Fixed Timestamp Formatting Tests
  SnapshotUtilsTest.testAppendCurrentTimestamp was throwing a NumberFormatException because the return value contained a UUID suffix (timestamp-UUID), but the test attempted to parse the entire string directly as a Long.
  Solution: Updated the test to split the string using the "-" character to extract and correctly parse just the timestamp prefix.
• Resolved Classpath and SPI Conflicts (dnsjava)
  Integration tests failed on Java 8 and 11 in Kokoro because of unshaded transitive dependency conflicts (com.google.protobuf.LiteralByteString NoClassDefFoundError).
  Solution: Reverted back to the shaded hbase-shaded-mapreduce dependency, ensuring proper compatibility across all Java versions.
• Uncommented and Fixed Tests in ImportJobFromHbaseSnapshotTest
  Several useful unit tests were commented out in ImportJobFromHbaseSnapshotTest because mockito-core lacked the ability to mock static methods.
  Solution:
  Switched from mockito-core to mockito-inline in the pom.xml to allow static mocking.
  Uncommented the code and restored the original formatting to prevent any lint errors, enabling JUnit to verify correct configuration parsing.

[tianlei2]

Integration test is run and passing:
https://fusion2.corp.google.com/invocations/33f68247-794b-45c2-8294-1b97ff42c5d0/artifacts/github%2Fjava-bigtable-hbase%2Fbigtable-dataflow-parent%2Fbigtable-beam-import%2Ftarget%2Ffailsafe-reports%2Fintegration-beam%2Fcom.google.cloud.bigtable.beam.hbasesnapshots.EndToEndIT;config=default