Fix a few bugs.

- Moving lines after themselves didnt work.
- moving empty lines deleted them.
- "w" didnt set state to unmodified in generic buffers.
- in "hl" aligned the numbers (by digits)

include/internal/buffer/decl.h

@@ -34,6 +34,7 @@ struct Buffer {
   virtual uint64_t bytes() = 0;
   virtual void set_filename(std::filesystem::path path) = 0;
   virtual std::filesystem::path filename() = 0;
+  virtual void saved_hook() = 0;
   virtual void load(BEd &ctx, vase::Shard *text) = 0;
   virtual vase::Shard *copy(uint64_t start_line, uint64_t end_line) = 0;
   virtual void substitute(

include/internal/buffer/types/clip.h

@@ -10,6 +10,7 @@ struct ClipBuffer : Buffer {
 
   void clip_write(vase::Shard *text);
   bool waste() override;
+  void saved_hook() override;
   uint64_t lines() override;
   uint64_t bytes() override;
   void load(BEd &ctx, vase::Shard *text) override;

include/internal/buffer/types/generic.h

@@ -31,6 +31,7 @@ struct GenericBuffer : ShardBuffer {
   bool undo(BEd &ctx);
   bool redo(BEd &ctx);
   uint64_t prune(int);
+  void saved_hook() override;
   bool waste() override;
   void load(BEd &ctx, vase::Shard *text) override;
   void set_filename(std::filesystem::path path) override;

include/internal/buffer/types/readonly.h

@@ -12,6 +12,7 @@ struct ReadonlyBuffer : ShardBuffer {
     const syntax::ParserSnapshot &snapshot
   ) : ShardBuffer(std::move(name), root, snapshot, Kind::History) {}
 
+  void saved_hook() override {}
   bool waste() override {
     return useless;
   }