Add explicit Unicode mode to regex patterns for proper Unicode handling (#40)

testdata/unicode_dot_regex.txt

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+# Test if . in regex matches Unicode characters
+exec echo "A✓B"
+stdout "A.B"

testdata/unicode_emoji.txt

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+# Test emoji in output
+exec echo "Status: 🎉 Success!"
+stdout "Status: 🎉 Success!"

testdata/unicode_grep.txt

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+# Test grep command with Unicode content
+grep "Success.*✓" test.txt
+stdout "test.txt:1: Success ✓"
+
+-- test.txt --
+Success ✓

testdata/unicode_multiple.txt

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+# Test multiple Unicode characters
+exec echo "Tests: ✓ ✗ ⚠ ℹ"
+stdout "Tests: ✓ ✗ ⚠ ℹ"

testdata/unicode_regex.txt

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+# Test Unicode in regex pattern
+exec echo "Success ✓ completed"
+stdout "Success .* completed"

testdata/unicode_special_chars.txt

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+# Test Unicode with regex special characters
+exec echo "Result: ✓ (success)"
+stdout "Result: ✓ \(success\)"

testdata/unicode_stderr.txt

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+# Test Unicode checkmark in stderr exact match
+exec sh -c 'echo "Error ✗" >&2'
+stderr "Error ✗"

testdata/unicode_stdout.txt

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+# Test Unicode checkmark in stdout exact match
+exec echo "Success ✓"
+stdout "Success ✓"