fix(derive): support container-level serde(default) in KubeSchema

[mrthinger]

Motivation

fix #1805

Combining KubeSchema with a bare container-level #[serde(default)] fails to compile. The derive generates mirror structs ({Name}Validated, plus a per-field Validated wrapper) to compute the schema, and copies the container serde attributes onto them. schemars turns the container default into <Self as Default>::default() calls on those mirrors, which don't implement Default, so the build fails with no function or associated item named `default` found for struct `MyCrdSpecValidated` .

Solution

Detect a bare container-level serde(default) and emit delegating Default impls for the generated mirrors. Each impl constructs the original type's default and moves the values into the mirror.

Since the per-field wrappers each construct the full original default and take one field from it, the original Default runs once per x_kube field (plus once for the full mirror) while generating the schema. This matches how serde sources missing fields from a container default, and only happens when the CRD is generated.

The default = "path" form already works, since schemars resolves the given function directly. A new test pins that behavior.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.9%. Comparing base (9981f58) to head (64c0332).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
kube-derive/src/cel_schema.rs	56.3%	7 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1999     +/-   ##
=======================================
+ Coverage   76.8%   76.9%   +0.1%     
=======================================
  Files         89      89             
  Lines       8813    8855     +42     
=======================================
+ Hits        6764    6801     +37     
- Misses      2049    2054      +5     

Files with missing lines	Coverage Δ
kube-derive/tests/crd_schema_test.rs	100.0% <100.0%> (ø)
kube-derive/src/cel_schema.rs	86.5% <56.3%> (-7.4%)	⬇️

... and 3 files with indirect coverage changes

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[Danil-Grigorev]

Hey! Looks good overall, nice change!

Just one request for test coverage, and naming for these macros. It would help longer term to orient in these changes.

[Danil-Grigorev]

Can you please add another field to the structure, so that test validates multiple defaulted values?

[Danil-Grigorev]

The naming is a bit confusing, since this is actually unwrapped original_default, I think it is better to shadow original_default with unwrapped value in this scope, or give it different name, like #default. Macros are harder to read overall, but this should improve it a bit.

Suggested change

	let original = #original;
	let original_default = #default;

[Danil-Grigorev]

Same as in https://github.com/kube-rs/kube/pull/1999/changes#r3407680513,

Suggested change

	let original = #original;
	let original_default = #default;