[common] Propagate checked IOException from RESTTokenFileIO#fileIO

[LuciferYang]

Purpose

close #9637

RESTTokenFileIO.fileIO() is declared throws IOException and then converted the one it gets into an unchecked wrapper:

try {
    fileIO = FileIO.get(path, context);
} catch (IOException e) {
    throw new UncheckedIOException(e);
}

So a data token that cannot produce an inner FileIO surfaced as UncheckedIOException from whichever FileIO call triggered the lazy creation, past every caller written for the declared signature. Two of those live outside paimon-common and can never run as things stand:

// paimon-lance LanceUtils, and the same shape in paimon-vortex VortexUtils
try {
    fileIO = ((RESTTokenFileIO) fileIO).fileIO();
} catch (IOException e) {
    throw new RuntimeException("Can't get fileIO from RESTTokenFileIO", e);
}

Letting the IOException through is all this needs. The signature does not change, so no caller has to, and the two above start reporting what they were written to report. The cache is keyed by RESTToken, so this path runs again on every token refresh rather than once at startup.

Tests

RESTTokenFileIOTest.testFileIOCreationFailureSurfacesAsCheckedIOException builds a RESTTokenFileIO over a scheme no loader can serve, with a unique token so the static token-keyed cache cannot hand back another test's delegate, and asserts that exists fails with an IOException.

Against the unfixed code that assertion fails on the type: what comes out is java.io.UncheckedIOException wrapping an UnsupportedSchemeException.

mvn -pl paimon-common -Dtest=RESTTokenFileIOTest test on JDK 8: 5 tests, 0 failures. spotless:check and checkstyle:check on paimon-common are clean.