feat(explorer): Git stats + Explorer Keymaps + Explorer line renderer

[richardgill]

This PR adds three related explorer features. They can be split into separate PRs if preferred.

Git line statistics

Optionally show per-file and aggregate insertion/deletion counts:

explorer = {
  line_stats = {
    enabled = true,
    count_untracked = false,
    max_untracked_bytes = 1024 * 1024,
  },
}

Files display +12 -4 or bin; folders and groups show aggregate totals. Statistics are disabled by default because they require additional Git queries.

Explorer line formatters

Replace complete file, folder, or group rows:

explorer = {
  formatters = {
    -- file = function(ctx) return layout end,
    -- folder = function(ctx) return layout end,
    group = function(ctx)
      return {
        left = {{
          segments = {{ text = " " .. ctx.label, hl = "CodeDiffExplorerTreeGroup" }},
          truncate_priority = 1,
        }},
        right = {{
          segments = {{ text = ctx.file_count .. " files", hl = "Number" }},
        }},
      }
    end,
  },
}

Formatters receive metadata for the represented files and return styled, left/right-aligned regions with display-width-aware truncation.

Custom explorer keymaps

Add buffer-local explorer actions:

keymaps = {
  explorer = {
    custom = {{
      key = "gy",
      desc = "Copy explorer path",
      callback = function(ctx)
        if ctx.entry.path then
          vim.fn.setreg("+", ctx.entry.path)
        end
      end,
    }},
  },
}

Callbacks receive the selected file, directory, or group, plus redraw() and refresh(). Custom mappings can override built-in explorer mappings.

Fixes #181
Fixes #455
Fixes #456

[esmuellert]

Thanks for the many fancy new features! I indeed would like it be multiple smaller PRs for easier review, and better risk management if there is a need for revert, thanks

[richardgill]

@esmuellert No problem 👍, here is a PR which just adds the explorer formatters: #472

[richardgill]

This has now been split into three focused PRs:

• feat(explorer): add configurable line formatters #472 - configurable Explorer line formatters (merged)
• feat(explorer): add optional Git line statistics #491 - optional Git line statistics (draft)
• feat(explorer): custom keymaps #492 - custom Explorer keymaps (draft)

Closing this combined PR in favor of those replacements.