Consider whitelisting code execution linters if argument is constant string

[mschwager]

Many of Dlint's checks looking for code execution bugs due to user input aren't insecure if its argument is a constant string. E.g. eval("2+2"). There are a few linters where this is the case:

$ rg 'constant string'
docs/linters/DUO120.md
36:* Code may be safe if data passed to `marshal` is a constant string

docs/linters/DUO119.md
36:* Code may be safe if data passed to `shelve` is a constant string

docs/linters/DUO106.md
41:* Code may be safe if data passed to `os.system` is a constant string

docs/linters/DUO103.md
36:* Code may be safe if data passed to `pickle` is a constant string

docs/linters/DUO104.md
35:* Code may be safe if data passed to `eval` is a constant string

docs/linters/DUO105.md
42:* Code may be safe if data passed to `exec` is a constant string

docs/linters/DUO110.md
43:* Code may be safe if data passed to `compile` is a constant string and limits data size

We should consider adding logic to these linters to prevent false positives when the argument is a constant string.