[#11813] fix(gvfs): override getScheme() to return 'gvfs'

[whua3]

FileSystem#getScheme() throws UnsupportedOperationException by default, which breaks Hadoop/Spark commit protocols (e.g. FileOutputCommitter, ManifestCommitter) when writing to a gvfs:// path. Override getScheme() in GravitinoVirtualFileSystem to return the GVFS scheme constant. Added unit test testGetScheme in TestGvfsBase.

What changes were proposed in this pull request?

Override getScheme() in GravitinoVirtualFileSystem to return the GVFS scheme constant (gvfs), instead of relying on the default org.apache.hadoop.fs.FileSystem#getScheme() which throws UnsupportedOperationException.

@Override
public String getScheme() {
  return GravitinoVirtualFileSystemConfiguration.GVFS_SCHEME;
}

Why are the changes needed?

Hadoop's default FileSystem#getScheme() throws UnsupportedOperationException if a subclass doesn't override it. Hadoop / Spark commit protocols call getScheme() during job setup / commit, so writing to a gvfs:// path currently fails. Returning the well-known gvfs scheme — which is already the URI scheme GVFS advertises and the value of GravitinoVirtualFileSystemConfiguration.GVFS_SCHEME — makes GVFS behave like every other Hadoop FileSystem implementation (LocalFS → file, HDFS → hdfs, S3A → s3a, …).

Fix: #11813

Does this PR introduce any user-facing change?

No public API change. FileSystem#getScheme() on a GravitinoVirtualFileSystem instance now returns "gvfs" instead of throwing. No new / removed configuration keys.

How was this patch tested?

Added a new unit test TestGvfsBase#testGetScheme that asserts fs.getScheme() equals GravitinoVirtualFileSystemConfiguration.GVFS_SCHEME. Ran ./gradlew :clients:filesystem-hadoop3:test locally and all tests pass.

[github-actions]

Code Coverage Report

Overall Project	67.23% +0.01%	🟢
Files changed	70.9%	🟢

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filesystem-hadoop3	77.3% -1.26%	🟢
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hadoop-common	10.88%	🔴
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Files

Module	File	Coverage
filesystem-hadoop3	GravitinoVirtualFileSystem.java	70.9%	🟢