merge local cobol_testgen improvements into v3 shared modules

- cond.py: SQLCODE/SQLSTATE handling, alphanumeric >/< boundary fix
- output.py: termination tracking, db_input support, _is_field_assigned filter
- coverage.py: mark_from_gcov, THRU support, KeyError protection
- gcov.py: new file (dependency for coverage.py)
- grammar.lark: multi-segment PIC support
- read.py: SQL INCLUDE resolution, DECLARE TABLE parsing, * comment fix
- core.py: SQL parsing, blocked_names, keyword list
- design.py: multi-sentinel, THRU ranges, PERFORM VARYING last iteration
- __init__.py: local main() + v3 API functions, guarded imports

All 6 ZAN programs verified passing through v3 pipeline

cobol_testgen/grammar.lark

@@ -13,7 +13,7 @@ clause: pic_clause | value_clause | occurs_clause | redefines_clause | usage_cla
       | "JUSTIFIED" "RIGHT"?
       | "BLANK" "WHEN" "ZERO"
       | "GLOBAL" | "EXTERNAL"
-pic_clause: "PIC" "IS"? PICTURE_STRING
+pic_clause: "PIC" "IS"? PICTURE_STRING ("." PICTURE_STRING)*
 value_clause: "VALUE" "IS"? value_literal+
 value_literal: INT | SIGNED_NUMBER | STRING | SQSTRING
              | "ZERO" | "ZEROS" | "ZEROES"