docs: replace native 'int' with core type 'uint16' in custom-codecs tutorial

[dimitri-yatsenko]

Summary

Replaces native database type int with core DataJoint type uint16 in the custom-codecs tutorial, following DataJoint 2.0 type system standards.

Changes

src/tutorials/advanced/custom-codecs.ipynb

• Cell 4 (Connectivity table): conn_id : int → conn_id : uint16
• Cell 9 (Unit table): unit_id : int → unit_id : uint16

Not changed:

• Cell 8: SpikeTrain.unit_id: int — This is a Python dataclass type annotation, not a DataJoint type, so it correctly remains int

Rationale

Per TERMINOLOGY.md and Type System specification:

Core DataJoint Types (Layer 2) - Preferred

• uint8, uint16, int32, float32, etc.
• Standardized, scientist-friendly
• Work identically across MySQL and PostgreSQL
• Include explicit size information

Native Database Types (Layer 1) - Discouraged

• INT, FLOAT, TINYINT UNSIGNED, etc.
• Backend-specific
• Generate warnings at declaration time
• Not portable, lack size metadata

Diff

Clean 2-line change:

-    conn_id : int
+    conn_id : uint16

-    unit_id : int
+    unit_id : uint16

Related

• User report: Found native type int at https://docs.datajoint.com/tutorials/advanced/custom-codecs/
• Follows best practices from Type System documentation

[dimitri-yatsenko]

Combined into PR #126