feat: develoment mode with hot-reloading

[fahdfady]

a step related to issue the development mode mentioned in issue #24
This adds

1. a new crate: metassr-watcher

2. a rebuilder module inside metassr-server crate

3. a new CLI command metassr dev

starts in package.json by building the project by running npm run build normally
enters a development mode

1. starts a normal server using `metassr-server
2. watches for changes in files: uses metassr-watcher crate to watcher for changes
3. Rebuilds on change (only for pages): if the watcher detected a change, rebuild

pub enum RebuildType {
    Page(PathBuf), // this only is doe
    Layout,
    Component,
    Style,
    Static,
}