Speed up boolean-token fallback in StringArray.getAsDouble

Replace the toLowerCase plus equals chain in the parse fallback with a
length-based dispatch: a single char compare for the 1-char "t"/"f"
tokens and compareToIgnoreCase for "true"/"false", matching the idiom
already used in DoubleArray.parseDouble. This avoids allocating a
lower-cased copy and rejects non-boolean strings immediately.

Restore throwing DMLRuntimeException on unparseable input. The previous
re-throw of the raw NumberFormatException changed the exception type and
broke callers such as Array.extractDouble that expect DMLRuntimeException;
the throw path is the genuinely-exceptional case, so the wrapping cost is
irrelevant there.

Author: Baunsgaard

src/main/java/org/apache/sysds/runtime/frame/data/columns/StringArray.java

@@ -610,14 +610,22 @@ private static double getAsDouble(String s) {
 			return DoubleArray.parseDouble(s);
 		}
 		catch(Exception e) {
-			String ls = s.toLowerCase();
-			if(ls.equals("true") || ls.equals("t"))
+			// Fallback for boolean-like tokens. Dispatch on length first so non-boolean strings are
+			// rejected immediately, and avoid allocating a lower-cased copy by comparing case-insensitively
+			// (single char compare for the 1-char tokens).
+			final int len = s.length();
+			if(len == 1) {
+				final char c = s.charAt(0);
+				if(c == 't' || c == 'T')
+					return 1;
+				else if(c == 'f' || c == 'F')
+					return 0;
+			}
+			else if(len == 4 && s.compareToIgnoreCase("true") == 0)
 				return 1;
-			else if(ls.equals("false") || ls.equals("f"))
+			else if(len == 5 && s.compareToIgnoreCase("false") == 0)
 				return 0;
-			else
-				throw e; // for efficiency
-				// throw new DMLRuntimeException("Unable to change to double: " + s, e);
+			throw new DMLRuntimeException("Unable to change to double: " + s, e);
 		}
 	}