chore: migrate package name to letta (#1775)

Co-authored-by: Charles Packer <packercharles@gmail.com>
Co-authored-by: Shubham Naik <shubham.naik10@gmail.com>
Co-authored-by: Shubham Naik <shub@memgpt.ai>

.gitignore

@@ -1,4 +1,4 @@
-# MemGPT config files
+# Letta config files
 configs/
 
 # Below are generated by gitignor.io (toptal)
@@ -387,7 +387,7 @@ __pycache__/
 .Python
 develop-eggs/
 downloads/
-eggs#memgpt/memgpt-server:0.3.7
+eggs#letta/letta-server:0.3.7
 MANIFEST
 
 # PyInstaller
@@ -1015,6 +1015,6 @@ pgdata/
 .persist/
 
 ## pytest mirrors
-memgpt/.pytest_cache/
+letta/.pytest_cache/
 memgpy/pytest.ini
 **/**/pytest_cache