Add ability to hide specific flags by setting their symbols to empty string

[Copilot]

This PR implements the ability to hide individual flags without disabling all flags, addressing the feature request for selective flag visibility.

Problem

Previously, flag display was all-or-nothing - users could only hide all flags or show all flags. There was no way to hide specific flag types (like stashes) while keeping others visible.

Solution

Following @arl's suggestion, flags are now completely hidden (including their counts) when their corresponding symbol is set to an empty string ("").

Examples

Before - stash count always visible when present:

symbols:
  stashed: "⚑ "  # Shows: ⚑ 3

After - stash count hidden by setting empty symbol:

symbols:
  stashed: ""    # Shows: (nothing)

This works for all flag types:

• staged: staged files count
• conflict: conflict files count
• modified: modified files count
• untracked: untracked files count
• stashed: stash entries count
• clean: clean status symbol

Implementation

• Modified the flags() method in tmux/formater.go to check for empty symbols before formatting flags
• Added comprehensive test coverage for all flag types with empty symbols
• Maintains backward compatibility - existing configurations continue to work unchanged

Fixes #115.

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[arl]

@copilot Simply make it so that if the symbol for a flag is empty, then we won't display it nor the count.

[Copilot]

@copilot Simply make it so that if the symbol for a flag is empty, then we won't display it nor the count.

Done! I've implemented exactly what you requested. The flags() method now checks if each symbol is empty, and when it is, that flag (including its count) won't be displayed.

All flag types are supported:

• staged, conflict, modified, untracked, stashed, clean

When any symbol is set to "", that specific flag is completely hidden while other flags continue to work normally.

Implementation is in commit a0c54a0 with comprehensive test coverage.

[arl]

LGTM!