[Fix] Fuzzy TCP: fix printf formats, buffer overflow, and timeout handling

[Fix] Fuzzy TCP: fix printf formats, buffer overflow, and timeout handling

- Fix printf format strings: use %ud instead of %u (rspamd printf requirement)
- Fix TCP write handler buffer overflow when writing frame header
  (ASAN error: remaining was calculated incorrectly)
- Fix timeout handling: mark commands as replied and check session completion
  to prevent task hanging on connection/request timeouts
- Fix Robot Framework test variables: add RSPAMD_ prefix for proper export
- Remove debug config dump