chore: update 3rd party libs (#766)

Dependency updates:

Updated several dependencies in conanfile.py, including catch2, json-schema-validator, libmaxminddb, openssl, pcapplusplus, sigslot, and libcurl to newer versions.
Code modernization in DNS layer:

Replaced all instances of NULL with nullptr in libs/visor_dns/DnsLayer.cpp to use modern C++ pointer semantics and improve code clarity and safety. This affects pointer initialization, comparisons, and return values throughout the file.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: leoparente

conanfile.py

@@ -7,29 +7,29 @@ class Pktvisor(ConanFile):
     generators = "CMakeToolchain", "CMakeDeps"
 
     def requirements(self):
-        self.requires("catch2/3.8.0")
+        self.requires("catch2/3.14.0")
         self.requires("corrade/2020.06")
         self.requires("cpp-httplib/0.18.3")
         self.requires("docopt.cpp/0.6.3")
         self.requires("fast-cpp-csv-parser/cci.20240102")
-        self.requires("json-schema-validator/2.3.0")
-        self.requires("libmaxminddb/1.10.0")
+        self.requires("json-schema-validator/2.4.0")
+        self.requires("libmaxminddb/1.12.2")
         self.requires("nlohmann_json/3.11.3")
-        self.requires("openssl/3.3.2")
+        self.requires("openssl/3.6.2")
         if self.settings.os != "Windows":
             self.requires("libpcap/1.10.5", force=True)
         else:
             self.requires("npcap/1.70")
         self.requires("opentelemetry-cpp/1.17.0")
-        self.requires("pcapplusplus/24.09")
+        self.requires("pcapplusplus/25.05")
         self.requires("protobuf/5.27.0")
-        self.requires("sigslot/1.2.2")
+        self.requires("sigslot/1.2.3")
         self.requires("fmt/10.2.1", force=True)
         self.requires("spdlog/1.15.0")
         self.requires("uvw/3.4.0")
         self.requires("yaml-cpp/0.8.0")
         self.requires("robin-hood-hashing/3.11.5")
-        self.requires("libcurl/8.11.1")
+        self.requires("libcurl/8.19.0")
         if (
             "libc" not in self.settings.compiler.fields
             or self.settings.compiler.libc != "musl"