Fenrir fixes

[mattia-moffa]

1861, 1863, 3020, 3730, 3942, 3943, 4399, 4400, 4401

[Copilot]

Pull request overview

This PR updates the Go wolfSSL bindings and wolftls transport to better support concurrent Read/Write on a single connection (when wolfSSL is built with write-dup support), along with related documentation/test updates and a few example/wrapper correctness fixes.

Changes:

• Add wolfSSL_write_dup-based split write handle in wolftls.Conn and serialize wolfSSL_read/wolfSSL_write with dedicated mutexes (or a shared mutex when write-dup isn’t available).
• Update docs/tests to reflect the --enable-writedup requirement for true concurrent Read+Write.
• Fix/adjust several examples and a wrapper helper (AES-GCM appended-tag encrypt output slicing).

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
wolfx509/certgen_wolfcrypt.go	Removes a custom cgo CFLAG define from the wolfx509 certgen binding build flags.
wolftls/tls_test.go	Skips the concurrent Read/Write test when write-dup support isn’t present.
wolftls/README.md	Documents --enable-writedup as a build requirement for concurrent Conn Read/Write.
wolftls/conn.go	Introduces sslWrite + muRead/muWrite to enable concurrent read/write when supported.
README.md	Updates wolfSSL build instructions to include --enable-writedup (currently presented as required).
examples/x509/extractKey.go	Adds WolfSSL_Init() and WolfSSL_Cleanup() calls around the example.
examples/x509/certVerify.go	Adds WolfSSL_Init() and WolfSSL_Cleanup() calls around the example.
examples/server/server.go	Exits on Accept() error to avoid continuing with an invalid connection.
examples/server/server-psk.go	Exits on Accept() error to avoid continuing with an invalid connection.
aes.go	Ensures the output slice length matches plaintext+tag size in appended-tag GCM encrypt.

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[lealem47]

Thank you @mattia-moffa !