## Summary
- Add non-blocking (incremental) Curve25519 key generation and shared secret via `WC_X25519_NONBLOCK`, modeled after the existing ECC non-blocking pattern (`WC_ECC_NONBLOCK`)
- Implement `curve25519_nb()` and `fe_inv__distinct_nb()` in `fe_low_mem.c` as state-machine variants that return `FP_WOULDBLOCK` to yield after each field multiply
- Add `wc_curve25519_set_nonblock()` API to attach/detach non-blocking context to a key
- Integrate X25519 non-blocking with TLS 1.2/1.3 key share generation and shared secret in `tls.c` and `internal.c` (behind `WC_X25519_NONBLOCK && WOLFSSL_ASYNC_CRYPT_SW`)
- Add `--enable-curve25519=nonblock` configure option (auto-enables `--enable-asynccrypt` and `--enable-asynccrypt-sw`)
- Add X25519 async software dispatch cases in `async.c` and types in `async.h`
- Fix async guard in `curve25519.c` to require `WOLFSSL_ASYNC_CRYPT_SW` (matching other algorithms)
- Overhaul `examples/async/` client/server: non-blocking I/O via `WOLFSSL_USER_IO`, standalone `Makefile`, X25519/ECC mode selection, CI-friendly ready-file sync
- Add `examples/configs/user_settings_curve25519nonblock.h` and CI coverage in `os-check.yml` and new `async-examples.yml` workflow
- Add wolfcrypt test and API test coverage for X25519 non-blocking
tests/api.c: add error_test() adapted from wolfcrypt/test/test.c, checking all error strings for expected presence/absence and length, called from existing test_wolfSSL_ERR_strings().
wolfssl/ssl.h, wolfssl/error-ssl.h, and wolfssl/wolfcrypt/error-crypt.h:
* move several negative error return codes from ssl.h to error-ssl.h,
* renumber them to conform to existing sequence, and
* include error-ssl.h from ssl.h;
* add special-case WOLFSSL_DEBUG_TRACE_ERROR_CODES macros for WOLFSSL_FAILURE;
* add missing WOLFSSL_API attribute to wc_backtrace_render().
add numerous WC_NO_ERR_TRACE()s to operand error code uses, cleaning up error traces in general, and particularly when WOLFSSL_DEBUG_TRACE_ERROR_CODES_ALWAYS.
* crypto lib (36),
* crypto test&benchmark (20),
* TLS lib (179),
* examples (122),
* linuxkm (3),
* tests/api.c (2272).
David Garske
JacobBarthelmeh
Daniel Pouzzner
Andras Fekete