feat: introduce hybrid signature framework and signature trailer builder

Add a complete hybrid signature implementation combining two independent
signature algorithms with AND/OR verification semantics, designed for
streaming pipelines.

Key changes:
- Add zeroecho.sdk.hybrid.signature package with core hybrid signature
  abstractions (HybridSignatureContext, HybridSignatureProfile,
  factories, predicates, and package documentation).
- Introduce SignatureTrailerDataContentBuilder as a
  signature-specialized replacement for
  TagTrailerDataContentBuilder<Signature>, supporting
  core, single-algorithm, and hybrid signature construction.
- Extend sdk.builders package documentation to reference the new
  signature trailer builder and newly added PQC signature builders.
- Adjust TagEngineBuilder where required to support hybrid verification
  integration.
- Update JUL configuration to accommodate hybrid signature diagnostics
  without leaking sensitive material.

Tests and samples:
- Add comprehensive JUnit 5 tests covering hybrid signatures in all
  supported modes, including positive and negative cases.
- Add a dedicated sample demonstrating hybrid signing combined with AES
  encryption (StE and EtS).
- Update existing signing samples to reflect the new signature trailer
  builder.

The changes introduce a unified, extensible hybrid signature model
without breaking existing core APIs or pipeline composition patterns.

Signed-off-by: Leo Galambos <lg@hq.egothor.org>

lib/src/main/resources/jul.properties

@@ -3,6 +3,7 @@ handlers = java.util.logging.ConsoleHandler
 
 zeroecho.core.tag.ByteVerificationStrategy.level = FINE
 zeroecho.core.tag.SignatureVerificationStrategy.level = FINE
+zeroecho.sdk.hybrid.signature.level = FINE
 
 # Console handler uses our one-line formatter
 java.util.logging.ConsoleHandler.level = ALL