feat(csvview): add event hooks for attach/detach

Added new events `CsvViewAttach` and `CsvViewDetach` to allow users
to hook into the attach and detach lifecycle of the CsvView. Updated
README with examples on how to use these events.

README.md

@@ -169,6 +169,28 @@ To toggle CSV view with a custom field delimiter, a custom string delimiter and
 - `require('csvview').toggle()`: Toggle CSV view.
 - `require('csvview').is_enabled()`: Check if CSV view is enabled.
 
+## Events
+
+This plugin provides the following events:
+
+- `CsvViewAttach`: Triggered after the initial metrics calculation is completed and the CsvView is attached.
+- `CsvViewDetach`: Triggered after the CsvView is detached.
+
+### Example
+
+You can hook into these events as follows:
+
+```lua
+local group = vim.api.nvim_create_augroup("CsvViewEvents", {})
+vim.api.nvim_create_autocmd("User", {
+  pattern = "CsvViewAttach",
+  group = group,
+  callback = function()
+    print("CsvView is attached")
+  end,
+})
+```
+
 ## Highlights
 
 | Group                | Default            | Description         |

lua/csvview/init.lua

@@ -31,9 +31,10 @@ function M.enable(bufnr, opts)
 
   local detach_bufevent_handle --- @type fun()
   local metrics = CsvViewMetrics:new(bufnr, opts)
-  local view = CsvView:new(bufnr, metrics, opts, function()
+  local view = CsvView:new(bufnr, metrics, opts, function() -- on detach
     detach_bufevent_handle()
     metrics:clear()
+    vim.api.nvim_exec_autocmds("User", { pattern = "CsvViewDetach" })
   end)
 
   -- Register buffer-update events.
@@ -54,6 +55,7 @@ function M.enable(bufnr, opts)
   -- Calculate metrics and attach view.
   metrics:compute_buffer(function()
     attach_view(bufnr, view)
+    vim.api.nvim_exec_autocmds("User", { pattern = "CsvViewAttach" })
   end)
 end