Accumulate SHA-1 digest across all class entries for the bytecode hash (#133)

[elharo]

Fixes #133

Problem

JarBytecodeHashAnalyzer.computeHash() overwrote result on each loop iteration, so the computed bytecode hash only covered the last class entry in the JAR:

for (JarEntry entry : entries) {
    try (InputStream is = jarAnalyzer.getEntryInputStream(entry)) {
        result = DigestUtils.sha1Hex(is); // overwrites previous result
    }
}

As a result, two JARs with completely different class sets could produce the same bytecodeHash whenever their last-sorted class entry was identical, contradicting the analyzer's contract of detecting an exact copy of the file's class data.

Fix

The SHA-1 digest is now updated incrementally across every class entry (in the stable, name-sorted order produced by JarAnalyzer), and the final digest is hex-encoded once after the loop.

Tests

Added JarBytecodeHashAnalyzerTest with two tests, both verified to fail before the fix and pass after:

• computeHashCoversAllClassEntries: the hash of codec.jar (14 classes) equals the SHA-1 of the concatenated class bytes.
• distinctClassSetsProduceDistinctHashes: two JARs sharing only the last-sorted class entry produce different hashes (they previously hashed identically).

[ppkarwasz]

LGTM

[github-actions]

@elharo Please assign appropriate label to PR according to the type of change.