ODB: following the 3DBlox "external" spec

[osamahammad21]

Describe the bug

The 3DBlox specification requires that each key under external maps to a YAML list of strings. In OpenROAD, we currently do not follow this requirement, as 'def_file` is assumed to be a single string rather than a list.

Expected Behavior

Parse all key values under the external map as a YAML list of strings. Produce an error if multiple DEF files are given saying that this multiple def files for the same chiplet is currently unsupported

Environment

NA

To Reproduce

try any 3dbx with this format:

ChipletInst:
  inst1:
    reference: master1
    is_master: true
    external:
      def_file:
      - master.def

Relevant log output

[ERROR ODB-0521] Parser Error: Error parsing value for def_file: yaml-cpp: error at line 15, column 7: bad conversion
[ERROR ODB-0521] Parser Error: DBX Error parsing YAML content: ODB-0521

Screenshots

No response

Additional Context

No response