Cache AEAD record overhead on WOLFSSL

[julek-wolfssl]

wolfssl_local_GetRecordSize() runs BuildMessage(sizeOnly=1) on every
wolfSSL_write hot path. For AEAD ciphers the overhead is constant per
connection framing state, so cache (recordSz - payloadSz) on WOLFSSL
and invalidate in SetKeysSide(), at cidInfo->tx assignment, and in
wolfSSL_clear(). BuildMessage stays the single source of truth.

Add test_record_size_matches_build_message (cross-checks every built
cipher over TLS/DTLS +/- CID against BuildMessage) and
test_record_size_cache_invalidated_on_renegotiation.

[Copilot]

Pull request overview

This PR optimizes the wolfSSL_write hot path by caching AEAD record framing overhead (derived from BuildMessage(sizeOnly=1)) per-connection, avoiding repeated BuildMessage() calls when the overhead is constant. The cache is invalidated on key/state transitions where record framing could change, and new API tests are added to cross-check sizing behavior against BuildMessage().

Changes:

• Add WOLFSSL::recordSzOverhead to cache AEAD (recordSz - payloadSz) overhead and use it in wolfssl_local_GetRecordSize().
• Invalidate the cache on cipher/key activation (SetKeysSide()), wolfSSL_clear(), and DTLS CID TX assignment.
• Add API tests that cross-check wolfssl_local_GetRecordSize() against BuildMessage(sizeOnly=1) across cipher suites and protocols.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
wolfssl/internal.h	Adds recordSzOverhead field to WOLFSSL for AEAD record overhead caching.
src/internal.c	Uses cached AEAD overhead in wolfssl_local_GetRecordSize() and populates cache on successful BuildMessage().
src/keys.c	Clears the cache in SetKeysSide() to invalidate on key/cipher activation.
src/dtls.c	Clears the cache when TX CID is assigned (record framing changes).
src/ssl.c	Clears the cache in wolfSSL_clear().
tests/api/test_tls.h	Registers new test declarations.
tests/api/test_tls.c	Adds record-size cross-check test and renegotiation invalidation test.

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[github-actions]

MemBrowse Memory Report

gcc-arm-cortex-m4

• FLASH: .text +64 B (+0.0%, 198,081 B / 262,144 B, total: 76% used)

gcc-arm-cortex-m4-tls12

• FLASH: .text +64 B (+0.1%, 121,501 B / 262,144 B, total: 46% used)
  No memory changes detected for:
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-min-ecc