Add Mbed TLS 4.x support (PSA Crypto) (#2502)

* Add Mbed TLS 4.x support (PSA Crypto) for macOS

Auto-detect Mbed TLS 4.x via MBEDTLS_VERSION_MAJOR and adapt the backend:
- Include psa/crypto.h and drop the headers removed in 4.x (ctr_drbg,
  entropy, md5, sha*), gated behind the version macro.
- Compute MD5/SHA-256/SHA-512 via PSA (psa_hash_compute) and initialize
  PSA Crypto once with std::call_once.
- Drop the explicit entropy/CTR-DRBG RNG (PSA provides the TLS RNG) and
  skip the RNG-callback overloads of pk_parse_key/pk_check_pair on 4.x.
- Retry on a TLS 1.3 NewSessionTicket (the 4.x default) in connect, read,
  write and is_peer_closed via a single mbedtls_is_session_ticket() helper,
  so online HTTPS works, including large redirected downloads where the
  ticket arrives mid-write.

Note V4 implies V3, so 3.x-only paths now check V3 && !V4.

Build systems (macOS): the CMake config and pkg-config shipped by Homebrew
resolve 4.x transitively, so CMakeLists.txt and meson.build need no change
for linking; the Makefile links libtfpsacrypto when present, else
libmbedcrypto.

Tests: generate the encrypted client key as both PBES2-AES (3.6+/4.x,
OpenSSL, wolfSSL) and PBES1-3DES (Mbed TLS 2.28) and pick by version, since
4.x dropped DES and 2.28 lacks PBES2. Also generate the IP-host certs in
test/meson.build to match gen-certs.sh and CMakeLists.txt.

* CI: test Mbed TLS 4.x on macOS, 3.x on Ubuntu 26.04

Homebrew's default mbedtls is now 4.x, so switch the macOS build and CI job
to it (drop the mbedtls@3 pin). That leaves 3.x (Ubuntu 24.04 apt ships 2.28,
macOS now 4.x) uncovered, so add an ubuntu-26.04 job whose apt provides Mbed
TLS 3.6. Net coverage: 2.28 (ubuntu-latest), 3.6 (ubuntu-26.04), 4.2 (macOS).

ubuntu-26.04 is a public-preview runner image; fold it into the main ubuntu
matrix once ubuntu-latest moves to 26.04.

* Document Mbed TLS 4.x support and libtfpsacrypto rename

Update README.md and the tour's TLS setup pages (en/ja) to note that
Mbed TLS 4.x is now auto-detected and that it renames libmbedcrypto
to libtfpsacrypto.

test/CMakeLists.txt

@@ -103,19 +103,32 @@ if(HTTPLIB_IS_USING_OPENSSL)
         WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
         COMMAND_ERROR_IS_FATAL ANY
     )
+    # Encrypted client key: make an unencrypted key + cert first, then wrap the
+    # same key two ways. Mbed TLS 4.x dropped DES/PBES1, while Ubuntu's Mbed TLS
+    # 2.28 has no PBES2-AES, so ship both and let test.cc pick by version.
     execute_process(
-        COMMAND ${OPENSSL_COMMAND} genrsa -aes256 -passout pass:test012! 2048
-        OUTPUT_FILE client_encrypted.key.pem
+        COMMAND ${OPENSSL_COMMAND} genrsa -out client_encrypted.tmp.key.pem 2048
         WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
         COMMAND_ERROR_IS_FATAL ANY
     )
     execute_process(
-        COMMAND ${OPENSSL_COMMAND} req -new -batch -config ${CMAKE_CURRENT_LIST_DIR}/test.conf -key client_encrypted.key.pem -passin pass:test012!
+        COMMAND ${OPENSSL_COMMAND} req -new -batch -config ${CMAKE_CURRENT_LIST_DIR}/test.conf -key client_encrypted.tmp.key.pem
         COMMAND ${OPENSSL_COMMAND} x509 -days 370 -req -CA rootCA.cert.pem -CAkey rootCA.key.pem -CAcreateserial
         OUTPUT_FILE client_encrypted.cert.pem
         WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
         COMMAND_ERROR_IS_FATAL ANY
     )
+    execute_process(
+        COMMAND ${OPENSSL_COMMAND} pkcs8 -topk8 -v2 aes-256-cbc -in client_encrypted.tmp.key.pem -passout pass:test012! -out client_encrypted.key.pem
+        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+        COMMAND_ERROR_IS_FATAL ANY
+    )
+    execute_process(
+        COMMAND ${OPENSSL_COMMAND} pkcs8 -topk8 -v1 PBE-SHA1-3DES -in client_encrypted.tmp.key.pem -passout pass:test012! -out client_encrypted_pbes1.key.pem
+        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+        COMMAND_ERROR_IS_FATAL ANY
+    )
+    file(REMOVE ${CMAKE_CURRENT_BINARY_DIR}/client_encrypted.tmp.key.pem)
     # Certificates for IP-host hostname verification regression tests.
     # cert_ip_cn.pem: CN is an IPv4 literal with NO subjectAltName. An IP host
     #                 must NOT be authenticated via the CN, so verifying it