docs: adversarial review round 9 for RFC-0202-A

Round 9 changes:
- M1: Added §6.8a stoolap_parse_decimal() function specification
- M2: Scientific notation rejection rationale in §6.8a
- M3: Added decimal_cmp to §2 import list
- M4: Removed duplicate per-query gas budget from Future Work
- L1: Fixed BIGINT overflow test vector (2^4096 overflows, 2^4095 is valid)
- L2: Added SHL/SHR test vectors (4 entries)
- L3: Leading zeros clarification in DECIMAL canonicalizes test

Author: mmacedoeu