fix: fix shell generation panic due to unnecessary 'conflicts_with'

[zilayo]

Problem

solana completions -s zsh currently panics when trying to generate zsh completions.

The root cause is the below code which defines a conflicting arg buffer_authority for solana program-v4 show, however buffer_authority is not an argument in program-v4 show:

agave/cli/src/program_v4.rs

Lines 277 to 283 in fc0183d

	.arg(
	Arg::with_name("all")
	.long("all")
	.conflicts_with("account")
	.conflicts_with("buffer_authority")
	.help("Show accounts for all authorities"),
	)

This results in clap panicking due to find_any_arg returning None, but the calling macro uses expect()

https://github.com/clap-rs/clap/blob/v2.33.3/src/completions/macros.rs#L15
https://github.com/clap-rs/clap/blob/v2.33.3/src/app/parser.rs#L2168-L2179

Summary of Changes

• Removed .conflicts_with("buffer_authority") from program-v4 show
• Added a unit test that ensures CLI completion works for all supported shells.

Fixes #2929

[t-nelson]

@pgarg66 it's supposed to be .conflicts_with("authority"), right?