refactor: breakdown twomap into multiple modules (#65)

* refactor: convert twomap.rs file into a cmap2 module

* refactor: move cmap tests into a dedicated file

* refactor: move struct & constructor definition to dedicated file

* refactor: move utils impl block to dedicated module

* refactor: move (un)sew/link methods to dedicated module

* refactor: move basic ops to dedicated module

* refactor: move vertex code to an embed module

this will also be the module that holds R/W code for generic attributes

* refactor: move some content to a common root module

* doc: add doc for each new private modules in cmap2/

Author: imrn99

honeycomb-core/src/cells/mod.rs

@@ -6,13 +6,3 @@
 
 pub mod collections;
 pub mod orbits;
-
-// ------ CONTENT
-
-/// Type definition for dart identifiers
-///
-/// This is used for better control over memory usage and ID encoding.
-pub type DartIdentifier = u32;
-
-/// Null value for dart identifiers
-pub const NULL_DART_ID: DartIdentifier = 0;