openssl: fix the data race when sharing an SSL session between threads

The SSL_Session object is mutated during connection inside openssl,
and it might not be thread-safe. Besides, according to documentation
of openssl:

```
SSL_SESSION objects keep internal link information about the session
cache list, when being inserted into one SSL_CTX object's session
cache. One SSL_SESSION object, regardless of its reference count,
must therefore only be used with one SSL_CTX object (and the SSL
objects created from this SSL_CTX object).
```
If I understand correctly, it is not safe to share it even in a
single thread.

Instead, serialize the SSL_SESSION before adding it to the cache,
and deserialize it after retrieving it from the cache, so that no
concurrent write to the same object is infeasible.

Also
 - add a ci test for thread sanitizer
 - add a test for sharing ssl sessions concurrently
 - avoid redefining memory functions when not building libcurl, but
   including the soruce in libtest
 - increase the concurrent connections limit in sws

Notice that there are fix for a global data race for openssl which
is not yet release. The fix is cherry pick for the ci test with
thread sanitizer.
d8def79838

Closes #14751

.github/workflows/linux.yml

@@ -149,6 +149,16 @@ jobs:
               --with-openssl --enable-debug --enable-websockets
             singleuse: --unit
 
+          - name: thread-sanitizer
+            install_packages: zlib1g-dev clang libtsan2
+            install_steps: pytest openssltsan3
+            configure: >
+              CC=clang
+              CFLAGS="-fsanitize=thread -g"
+              LDFLAGS="-fsanitize=thread -Wl,-rpath,$HOME/openssl3/lib"
+              --with-openssl=$HOME/openssl3 --enable-debug --enable-websockets
+            singleuse: --unit
+
           - name: memory-sanitizer
             install_packages: clang
             install_steps:
@@ -310,6 +320,28 @@ jobs:
           ./config --prefix=$HOME/openssl3 --libdir=lib
           make -j1 install_sw
 
+      - name: cache openssltsan3
+        if: contains(matrix.build.install_steps, 'openssltsan3')
+        uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9 # v4
+        id: cache-openssltsan3
+        env:
+          cache-name: cache-openssltsan3
+        with:
+          path: /home/runner/openssl3
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ env.openssl3-version }}-d8def798
+
+      - name: 'install openssltsan3'
+        if: contains(matrix.build.install_steps, 'openssltsan3') && steps.cache-openssltsan3.outputs.cache-hit != 'true'
+        # There are global data race in openssl:
+        # Cherry-Pick the fix for testing https://github.com/openssl/openssl/pull/24782
+        run: |
+          git clone --quiet --depth=1 -b ${{ env.openssl3-version }} https://github.com/openssl/openssl
+          cd openssl
+          git fetch --quiet --depth=2 origin d8def79838cd0d5e7c21d217aa26edb5229f0ab4
+          git cherry-pick -n d8def79838cd0d5e7c21d217aa26edb5229f0ab4
+          CC="clang" CFLAGS="-fsanitize=thread" LDFLAGS="-fsanitize=thread" ./config --prefix=$HOME/openssl3 --libdir=lib
+          make -j1 install_sw
+
       - name: cache quictls
         if: contains(matrix.build.install_steps, 'quictls')
         uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9 # v4