Introducelf.structured.complete with enhanced Python schema support.

[copybara-service]

Introducelf.structured.complete with enhanced Python schema support.

Usage:

class Person:
  name: str
  birth_place: str
  birth_year: int
  
lf.complete(Person.partial('Larry Page'), lm=lf.llms.Gpt35())

This CL also:

• Update the default LM timeout from 30 to 120 seconds.
• lf.MISSING and lf.UNKNOWN for representing missing and unknown fields.

[codecov-commenter]

Codecov Report

Merging #7 (6a46e99) into main (03643b4) will increase coverage by 0.22%.
The diff coverage is 97.98%.

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   96.57%   96.80%   +0.22%     
==========================================
  Files          33       34       +1     
  Lines        2305     2470     +165     
  Branches      490      516      +26     
==========================================
+ Hits         2226     2391     +165     
  Misses         33       33              
  Partials       46       46              

Files Changed	Coverage Δ
langfun/core/language_model.py	96.87% <ø> (ø)
langfun/core/structured/nl2structure.py	88.23% <ø> (ø)
langfun/core/structured/schema.py	95.92% <97.64%> (+1.09%)	⬆️
langfun/core/structured/structure2structure.py	98.46% <98.46%> (ø)
langfun/__init__.py	100.00% <100.00%> (ø)
langfun/core/structured/__init__.py	100.00% <100.00%> (ø)
langfun/core/structured/mapping.py	97.72% <100.00%> (-0.06%)	⬇️

... and 1 file with indirect coverage changes