Implement network and advanced condition support

Co-authored-by: imjasonh <210737+imjasonh@users.noreply.github.com>

testdata/env_conditions.txt

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+# Test environment variable conditions
+
+# Set an env var in the test
+env TEST_VAR=hello
+
+# This should execute since TEST_VAR is now set
+[env:TEST_VAR] exec echo "Environment variable TEST_VAR is set"
+[env:TEST_VAR] stdout "Environment variable TEST_VAR is set"
+
+# This should be skipped since MISSING_VAR is not set
+[env:MISSING_VAR] exec echo "This should not appear"
+
+# This should execute since MISSING_VAR is not set (negated condition)
+[!env:MISSING_VAR] exec echo "MISSING_VAR is not set (as expected)"
+[!env:MISSING_VAR] stdout "MISSING_VAR is not set (as expected)"
+
+# Test PATH environment variable which should exist on all systems
+[env:PATH] exec echo "PATH environment variable exists"
+[env:PATH] stdout "PATH environment variable exists"

testdata/network_conditions.txt

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+# Test network condition support
+
+# This command will only run if network is available
+[net] exec echo "Network is available"
+
+# This command will only run if network is not available  
+[!net] exec echo "Network is not available"
+
+# At least one of the above should execute, so we should see some output
+exec echo "Network test completed"
+stdout "Network test completed"

testdata/program_conditions.txt

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+# Test program detection conditions
+
+# Test that echo is available (should work on all platforms)
+[exec:echo] exec echo "echo command is available"
+[exec:echo] stdout "echo command is available"
+
+# Test negation for a program that shouldn't exist
+[!exec:nonexistent_program_xyz123] exec echo "nonexistent program not found"  
+[!exec:nonexistent_program_xyz123] stdout "nonexistent program not found"
+
+# Test built-in program detections that are set by default
+[exec:ls] exec echo "ls command detected"
+[exec:mkdir] exec echo "mkdir command detected"
+
+# At least mkdir should work since it's tested
+[exec:mkdir] stdout "mkdir command detected"