Remove some unsafe annotations.

src/core/Terminals/Unix/Linux/LinuxVirtualTerminal.cs

@@ -96,7 +96,7 @@ public override int OpenTerminalHandle(string name)
         return open(name, O_RDWR | O_NOCTTY | O_CLOEXEC);
     }
 
-    public override unsafe bool PollHandles(int? error, short events, scoped Span<int> handles)
+    public override bool PollHandles(int? error, short events, scoped Span<int> handles)
     {
         if (error is int err && err != EAGAIN)
             return false;

src/core/Terminals/Unix/MacOS/MacOSVirtualTerminal.cs

@@ -96,7 +96,7 @@ public override int OpenTerminalHandle(string name)
         return open(name, O_RDWR | O_NOCTTY | O_CLOEXEC);
     }
 
-    public override unsafe bool PollHandles(int? error, short events, scoped Span<int> handles)
+    public override bool PollHandles(int? error, short events, scoped Span<int> handles)
     {
         if (error is int err && err != EAGAIN)
             return false;

src/core/Terminals/Unix/UnixTerminalReader.cs

@@ -20,7 +20,7 @@ public UnixTerminalReader(
         _cancellationPipe = cancellationPipe;
     }
 
-    protected override unsafe int ReadPartialCore(scoped Span<byte> buffer, CancellationToken cancellationToken)
+    protected override int ReadPartialCore(scoped Span<byte> buffer, CancellationToken cancellationToken)
     {
         using var guard = Terminal.Control.Guard();
 

src/core/Terminals/Unix/UnixTerminalWriter.cs

@@ -12,7 +12,7 @@ public UnixTerminalWriter(UnixVirtualTerminal terminal, string name, int handle,
         _semaphore = semaphore;
     }
 
-    protected override unsafe int WritePartialCore(
+    protected override int WritePartialCore(
         scoped ReadOnlySpan<byte> buffer, CancellationToken cancellationToken)
     {
         using var guard = Terminal.Control.Guard();