no_std compilation broken in v0.25.0

[RAprogramm]

Problem

v0.25.0 fails to compile without default features (no_std mode):

error[E0412]: cannot find type `String` in `builder.rs:126,416`
error[E0412]: cannot find type `Box` in `introspection.rs:238`
error[E0599]: no method `to_string` in `display.rs:391`

Root Cause

Missing alloc imports when std feature is disabled.

Solution

1. Add use alloc::string::String; to builder.rs
2. Add use alloc::boxed::Box; to introspection.rs
3. Add use alloc::string::ToString; to display.rs
4. Add CI check: cargo check --no-default-features

Severity

Critical - Breaks no_std builds

Hotfix

Will release v0.25.1