Few optimizations to `CatfishSearchEngine.py` for better performance and lesser memory usage

I think we can slightly optimize catfish

1. The else block at line 292 in method CatfishSearchEngine.search_filenames in CatfishSearchEngine.py

   # OLD
   match_list = set()
   for kword in keywords:
       if kword in fname.lower():
           match_list.add(kword)
       if len(set(keywords)) == len(match_list):
           return True
   
   # NEW
   # Avoids repeated substring search for duplicates in `keywords`
   # Avoids repeated processing of converting `fname` to lower case
   # Avoids repeated conversion of object `keywords` to `set`
   # No need of an extra `set` data structure `match_list` (thus reducing memory usage)
   # Returns immediately if a single `kword` is not present in `fnanme`
   fname = fname.lower()
   for kword in set(keywords):
       if kword not in fname:
           return False
   return True

2. In method CatfishSearchMethod_Zeitgeist.run at line 674 of CatfishSearchEngine.py
   • This change avoid repeated conversion of string keywords to lower case in nested for loops

   # line=676
   
   # OLD
   keywords = " ".join(keywords)
   
   # NEW
   keywords = " ".join(keywords).lower()

   # line=707
   
   # OLD
   if keywords.lower() in filename and \
   
   # NEW
   if keywords in filename and \

3. else block of method CatfishSearchMethod_Fulltext.search_text at line 557 of CatfishSearchEngine.py
   • I did some performance testing using the attached files optimization3_.* and found that the proposed change indeed improved the performance. Following are some of the results
     • optimization3_speed_test.py
     • optimization3_speed_test_input_generator.py

     [ExecutionTime] "catfish_old_full_search" = 00:00:08.600 (i.e. ~8 seconds)
     [ExecutionTime] "new_full_search" = 00:00:00.285 (~0.29 seconds)
     
     [ExecutionTime] "catfish_old_full_search" = 00:00:00.935 (i.e. ~0.9 seconds)
     [ExecutionTime] "new_full_search" = 00:00:00.128 (i.e. ~0.13 seconds)

   # OLD
   def search_text(self, lines, keywords):
       if self.exact:
           for line in lines:
               if " ".join(keywords) in line.lower():
                   return True
       else:
           match_list = set()
           for line in lines:
               for kword in keywords:
                   if kword in line.lower():
                       match_list.add(kword)
               if len(set(keywords)) == len(match_list):
                   return True
   
   # NEW
   # Avoids repeated substring search for duplicates in `keywords`
   # Avoids repeated conversion of `keywords` object to `set`
   # Avoids repeated substring search if the keyword was already found in the past
   # Extra memory requirement has reduced from `set[str]` to `bool array + int`
   def search_text(self, lines, keywords):
       if self.exact:
           for line in lines:
               if " ".join(keywords) in line.lower():
                   return True
       else:
           keywords = list(set(keywords))
           match_found = [False for i in range(len(keywords))]
           match_found_count = 0
           for line in lines:
               for i in range(len(keywords)):
                   if (not match_found[i]) and keywords[i] in line.lower():
                       match_found[i] = True
                       match_found_count += 1
               if match_found_count == len(keywords):
                   return True