feat(csharp/Benchmarks): Add .NET Framework 4.7.2 support with TLS co… (#3682)

This commit enhances the CloudFetch benchmark suite to support testing
on .NET Framework 4.7.2, which is the runtime used by Power BI. There
are some notable difference in .NET472 vs .NET8.0, one of them is
/K4os.Compression.LZ4 use the DefaultArrayPool in .NET472 which has a 1
MB upper limit for array size, where .NET8.0 use the SharedArrayPool
which almost have no size limit.

Changes:
- Add net472 target framework to Benchmarks.csproj
- Make Tests project reference conditional (net8.0 only, since Tests
doesn't support net472)
- Enable TLS 1.2/1.3 in CloudFetchBenchmarkRunner for .NET Framework
- Enable TLS 1.2/1.3 in benchmark GlobalSetup for spawned processes

These changes are necessary because .NET Framework 4.7.2 doesn't enable
modern TLS protocols by default, which are required for Databricks HTTPS
connections. This allows accurate performance testing on the Power BI
runtime environment (net472 with DefaultArrayPool).

Command:
` dotnet run -c Release --project Benchmarks/Benchmarks.csproj
--framework net472 CloudFetchBenchmarkRunner`
Sample output: 
| Method | ReadDelayMs | Mean | Min | Max | Median | Peak Memory (MB) |
Total Rows | Total Batches | Gen0 | Gen1 | Gen2 | Allocated |
|------------------ |------------
|--------:|--------:|--------:|--------:|-----------------:|-----------:|--------------:|------------:|-----------:|-----------:|----------:|
| ExecuteLargeQuery | 5 | 9.659 s | 9.016 s | 10.03 s | 9.928 s | 356.38
| 1,439,935 | 740 | 336000.0000 | 57000.0000 | 35000.0000 | 2.73 GB |


🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

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

Author: eric-wang-1990

csharp/Benchmarks/Benchmarks.csproj

@@ -2,7 +2,8 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>net8.0</TargetFrameworks>
+    <TargetFrameworks Condition="'$(IsWindows)'=='true'">net8.0;net472</TargetFrameworks>
+    <TargetFrameworks Condition="'$(TargetFrameworks)'==''">net8.0</TargetFrameworks>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <ProcessArchitecture>$([System.Runtime.InteropServices.RuntimeInformation]::ProcessArchitecture.ToString().ToLowerInvariant())</ProcessArchitecture>

csharp/Benchmarks/CloudFetchBenchmarkRunner.cs

@@ -19,6 +19,9 @@
 using BenchmarkDotNet.Columns;
 using BenchmarkDotNet.Configs;
 using BenchmarkDotNet.Running;
+#if NET472
+using System.Net;
+#endif
 
 namespace Apache.Arrow.Adbc.Benchmarks
 {
@@ -30,6 +33,10 @@ public class CloudFetchBenchmarkRunner
     {
         public static void Main(string[] args)
         {
+#if NET472
+            // Enable TLS 1.2/1.3 for .NET Framework 4.7.2 (required for modern HTTPS endpoints)
+            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | (SecurityProtocolType)3072; // 3072 = Tls13
+#endif
             // Configure to include the peak memory column and hide confusing error column
             var config = DefaultConfig.Instance
                 .AddColumn(new PeakMemoryColumn())

csharp/Benchmarks/Databricks/CloudFetchRealE2EBenchmark.cs

@@ -29,6 +29,9 @@
 using BenchmarkDotNet.Columns;
 using BenchmarkDotNet.Reports;
 using BenchmarkDotNet.Running;
+#if NET472
+using System.Net;
+#endif
 
 namespace Apache.Arrow.Adbc.Benchmarks.Databricks
 {
@@ -127,6 +130,10 @@ public class CloudFetchRealE2EBenchmark
         [GlobalSetup]
         public void GlobalSetup()
         {
+#if NET472
+            // Enable TLS 1.2/1.3 for .NET Framework 4.7.2 (required for modern HTTPS endpoints)
+            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | (SecurityProtocolType)3072; // 3072 = Tls13
+#endif
             // Check if Databricks config is available
             string? configFile = Environment.GetEnvironmentVariable("DATABRICKS_TEST_CONFIG_FILE");
             if (string.IsNullOrEmpty(configFile))