fix tracking issue with lazy filled attributes

[Surya2k1]

Currently there is an issue with Tracking when for custom layers the attributes initialized empty and assigned with empty values that filled at later stage. This PR addresses the same.

Fixes #20598

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 66.54%. Comparing base (a25881c) to head (8ce1866).

Files with missing lines	Patch %	Lines
keras/src/utils/tracking.py	83.33%	0 Missing and 1 partial ⚠️

❗ There is a different number of reports uploaded between BASE (a25881c) and HEAD (8ce1866). Click for more details.

HEAD has 6 uploads less than BASE

Flag	BASE (a25881c)	HEAD (8ce1866)
keras	5	2
keras-numpy	1	0
keras-torch	1	0
keras-jax	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #20783       +/-   ##
===========================================
- Coverage   82.01%   66.54%   -15.47%     
===========================================
  Files         555      555               
  Lines       51856    51868       +12     
  Branches     8021     8027        +6     
===========================================
- Hits        42530    34517     -8013     
- Misses       7377    15543     +8166     
+ Partials     1949     1808      -141     

Flag	Coverage Δ
keras	66.51% <91.66%> (-15.33%)	⬇️
keras-jax	?
keras-numpy	?
keras-openvino	29.91% <16.66%> (-0.01%)	⬇️
keras-tensorflow	64.75% <91.66%> (+<0.01%)	⬆️
keras-torch	?

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.