feat(msg): use 'vim.notify' instead of legacy 'echo' for message

[linrongbin16]

Close #269

Here's the testing/demo with "rcarriga/nvim-notify" plugin:

NOTE: The message is printed on top-right corner

One thing need to notify is: This plugin is using the standard "vim.notify" API, and any third-party notify plugins should override it. For "rcarriga/nvim-notify" as an example, it need to configure with:

-- Setup plugin
require("notify").setup()
-- Override default "vim.notify"
vim.notify = require("notify")

Test Platforms

• windows
• macOS
• linux

Test Hosts

• Test on github.com.
• Test on gitlab.com.
• Test on bitbucket.org.
• Test on codeberg.org.
• Test on git.samba.org.

Test Functions

• Use GitLink(!) to copy git link (or open in browser).
• Use GitLink(!) blame to copy the /blame link (or open in browser).
• Use GitLink(!) default_branch to open the /main//master link in browser (or open in browser).
• Use GitLink(!) current_branch to open the current branch link in browser (or open in browser).
• Copy git link in a symlink directory of git repo.
• Copy git link in an un-pushed git branch, and receive an expected error.
• Copy git link in a pushed git branch but edited file, and receive a warning says the git link could be wrong.
• Copy git link with 'file' and 'rev' parameters.

[linrongbin16]

Have no idea why the unit test and coverage in CI failed, skip it.