feat: add into_status_default() convenience method

[ae2rs]

Summary

• Adds a default method into_status_default() to the IntoStatus trait that calls into_status(&EncodeOptions::default()), eliminating the need for callers to construct default options explicitly
• Updates the basic.rs example to demonstrate both the explicit and convenience forms
• Updates the crate-level doc example (quick-start) to use the shorter form
• Bumps workspace version from 0.6.3 to 0.6.4

Details

This is a purely additive, non-breaking change. The new default method on the trait means all existing IntoStatus implementors get into_status_default() for free — no manual implementation required.

Before:

let status = err.into_status(&EncodeOptions::default());

After:

let status = err.into_status_default();

The explicit into_status(&opts) form remains available for callers who need custom encode options.

Test plan

• cargo test --workspace — all 51 tests pass (including updated doc-test)
• CI: rustfmt, clippy, MSRV 1.85, full test suite

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