v4: Fix Fortinet driver swap_negation and idempotent_for bugs

[jtdub]

Description

Two bugs in the Fortinet FortiOS driver:

1. swap_negation() drops parameters (driver.py:47)

child.text = f"{self.negation_prefix}{child.text.removeprefix(self.declaration_prefix).split()[0]}"

.split()[0] keeps only the first word after the prefix, dropping all parameters:

• Input: set description "Port 1" → unset description (drops "Port 1")

2. idempotent_for() IndexError (driver.py:61)

config.text.split()[1] == other_child.text.split()[1]

No bounds check — crashes with IndexError on single-word commands (e.g., bare set).

Proposed Fix

1. Preserve full command text in swap_negation() (like VyOS driver does)
2. Add bounds check before .split()[1] access

These should ideally be addressed alongside #220 (unified negation rules) and #222 (declarative-only drivers) in v4.