Basically add DID support

docs/roadmap.md

···
 |OAuth||
 |Event Stream||
 |Sync||
-|DID||
+|DID|Only implements data model part.|
 |Handle||
 |NSID||
 |TID|`tid` Done, however not implemented to Data Model and Lexicon|

src/atpasser/did/__init__.py

···
+import re
+
+
+class DID:
+    """
+    A class representing a DID.
+
+    Attributes:
+        uri (str): The DID URI.
+    """
+    def __init__(self, uri: str) -> None:
+        """
+        Initalizes an DID object.
+
+        Parameters:
+            uri (str): The DID URI.
+        """
+        pattern = re.compile("^did:[a-z]+:[a-zA-Z0-9._:%-]*[a-zA-Z0-9._-]$")
+        patternMatch = pattern.match(uri)
+        if patternMatch and len(uri) <= 2048:
+            self.uri = patternMatch[0]
+        else:
+            raise ValueError
+
+    def __str__(self) -> str:
+        """
+        Convert the TID to a string by given the URI.
+        """
+        return self.uri
+
+    def __eq__(self, value: object, /) -> bool:
+        """
+        Check if the 2 values are exactly the same.
+        """
+        if isinstance(value, DID):
+            return str(self) == str(value)
+        else:
+            raise TypeError