Add downstream version requirement helper

[codeforester]

Summary

Add a Base-native helper that lets downstream scripts require a minimum base-bash-libs version at runtime.

Rationale

The library already exposes BASE_BASH_LIBS_VERSION; consumers also need a small, documented way to fail clearly when a script depends on newer public APIs. This borrows the concept of explicit minimum-version checks from external Bash stdlib designs without copying their implementation.

Proposed Scope

• Add a public helper in lib/bash/std/lib_std.sh, such as base_bash_libs_require_version <minimum_version>.
• Compare semantic-ish dotted versions without depending on external commands.
• Emit a clear fatal error when the loaded library is too old.
• Document the helper in the std README and top-level usage examples.
• Add focused BATS coverage for equal, newer, older, and invalid version inputs.

Acceptance Criteria

• Downstream scripts can check a minimum supported base-bash-libs version after sourcing lib_std.sh.
• Invalid or unsupported version strings fail clearly.
• ./tests/validate.sh passes.

Notes

Concept source: comparison with srcshelton/stdlib.sh; write fresh Base-style code under this repo's standards.