DTLS 1.3 write dup support

[julek-wolfssl]

• Copy TLS 1.3 traffic secrets and DTLS 1.3 epoch/cipher state to the
  write-dup side in DupSSL so key updates can be performed.
• Delegate KeyUpdate responses from the read side to the write side via
  the shared WriteDup struct, for both peer-initiated and local key
  updates.
• Delegate DTLS 1.3 ACK sending from the read side to the write side.
• Track DTLS 1.3 KeyUpdate ACKs: write side records the in-flight
  KeyUpdate epoch/seq, read side sets keyUpdateAcked when the matching
  ACK arrives.
• Delegate post-handshake certificate authentication (CertificateRequest
  processing) from the read side to the write side, transferring
  transcript hashes, cert context, and signature parameters.
• Reset prevSent/plainSz to prevent stale values from SendData to think
  that data was already sent.
• Refactor FreeHandshakeHashes into Free_HS_Hashes for reuse.
• Move DTLS 1.3 epoch initialization earlier in InitSSL so the
  write-dup early-return path has valid epoch state.
• Add tests for write dup with all protocol versions, key update,
  post-handshake auth, and WANT_WRITE recovery.
• Add --enable-all --enable-writedup to CI os-check matrix.

[Copilot]

Pull request overview

Adds DTLS 1.3/TLS 1.3 write-dup (DupSSL) support so the read-side can delegate post-handshake work (KeyUpdate responses, DTLS13 ACK sending, post-handshake auth) to the write-side, along with new tests and CI coverage.

Changes:

• Extend WriteDup shared state to transfer DTLS13 ACKs, track KeyUpdate ACKs, and delegate post-handshake auth state.
• Update TLS13/DTLS13 processing to delegate write-required actions from read-dup to write-dup.
• Add/expand API tests for write-dup across protocol versions, WANT_WRITE recovery paths, key updates, and post-handshake auth; enable writedup config in CI.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
wolfssl/internal.h	Adds new write-dup shared fields/flags and new internal function declarations used by delegation paths.
src/internal.c	Refactors handshake-hash freeing for reuse and moves DTLS13 epoch init earlier for write-dup early returns.
src/tls13.c	Delegates TLS 1.3 KeyUpdate response and post-handshake CertificateRequest handling to write-dup side.
src/dtls13.c	Delegates DTLS 1.3 ACK work to write-dup and tracks KeyUpdate ACK arrival; exposes RTX removal helper.
src/ssl.c	Copies TLS13 secrets/DTLS13 epoch state into dup; implements write-side execution of delegated work.
tests/api.c	Adds/expands tests for write-dup across TLS/DTLS versions, key updates, post-handshake auth, WANT_WRITE.
.github/workflows/os-check.yml	Adds --enable-all --enable-writedup to CI matrix to exercise the new feature.

Comments suppressed due to low confidence (3)

src/internal.c:1

• Free_HS_Hashes is declared as WOLFSSL_LOCAL in wolfssl/internal.h, but the definition here omits WOLFSSL_LOCAL, which can cause a linkage/visibility mismatch depending on how WOLFSSL_LOCAL is defined. Update the definition to match the header's storage/visibility macro. Also, setting hsHashes = NULL at the end has no effect on the caller (pass-by-value), so either remove that line or change the API to take HS_Hashes** if caller-nullification is required.
  src/internal.c:1
• Free_HS_Hashes is declared as WOLFSSL_LOCAL in wolfssl/internal.h, but the definition here omits WOLFSSL_LOCAL, which can cause a linkage/visibility mismatch depending on how WOLFSSL_LOCAL is defined. Update the definition to match the header's storage/visibility macro. Also, setting hsHashes = NULL at the end has no effect on the caller (pass-by-value), so either remove that line or change the API to take HS_Hashes** if caller-nullification is required.
  tests/api.c:1
• EXCHANGE_DATA is defined multiple times in this file with very similar bodies (including WANT_WRITE variants). This increases the chance of tests diverging unintentionally when the exchange logic needs updating. Consider using a small helper function (or a single parameterized macro) that takes the relevant ssl handles/test context flags to centralize the exchange behavior.

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