fix: Allow reading from special files (device, FIFO, etc)

[theasp]

See: #884

Don't check to see if the filename is a normal file as it will prevent reading from other types of files. Only directories are treated differently.

FIFO:

industrial:~/projects/aichat$ target/debug/aichat -f <(echo I am a banana)
 It seems like you're trying to share some information or engage in a conversation. However, the text "I am a banana" doesn't provide much context for me to respond to
effectively. If you have any specific questions or topics you'd like to discuss, feel free to let me know!

File:

industrial:~/projects/aichat$ target/debug/aichat -f LICENSE-MIT "What license is this?"
 The provided text is the MIT License. Here are some key points about it:
[...]

Device:

industrial:~/projects/aichat$ target/debug/aichat -f /dev/null
 The term `/dev/null` is a special file in Unix-like operating systems, including Linux and macOS. It's often referred to as the "bit bucket" or the "black hole." Here are
some key points about `/dev/null`:
[...]

Directory:

industrial:~/projects/aichat$ target/debug/aichat -f scripts "How many files have you read?"
 Based on the provided files, it appears that you have implemented shell completions and integrations for a command-line tool named `aichat`. The completions are available
for multiple shell environments including PowerShell (`aichat.ps1`), Zsh (`aichat.zsh`), Fish (`aichat.fish`), Bash (`aichat.bash`), and Nushell (`aichat.nu`).
Additionally, there are shell integration scripts for these environments to facilitate real-time interaction with `aichat`.

[theasp]

Thanks!