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>
