Add portable field physical metadata to OSI

[deepralhan26]

OSI Field Physical Metadata Proposal

OSI currently has no first-class place to store basic field physical metadata such as datatype and nullability. That makes import/export and validation harder for systems that already expose these properties directly, and it pushes broadly useful metadata into vendor extensions.

Proposal

Add an optional Field.physical block to OSI:

physical:
  data_type: decimal
  nullable: true
  precision: 18
  scale: 2
  format: "#,##0.00"

Schema

Property	Type	Required	Description
data_type	string	✅	The physical data type of the field
nullable	boolean	✅	Whether the field accepts null values
precision	integer	❌	Total number of significant digits
scale	integer	❌	Number of digits to the right of the decimal point
format	string	❌	Display or serialization format string