Tags: vixcpp/env

Merge dev

feat(env): introduce env module with .env parsing, layered loading an…

…d typed access

- add process environment API (has, get, get_or, set, unset)
- add typed getters (bool, int, uint, double)
- add .env parsing (parse_line, parse_content)
- add file loading (load_file)
- add layered env support (.env, .env.local, .env.<env>, .env.<env>.local)
- add resolver for env file paths
- add process injection (load_into_process, load_layered_into_process)

- introduce EnvFile, EnvFileOptions and EnvResult types
- integrate with vix_error (Result<T>, ErrorCode, ErrorCategory)

- add comprehensive test suite (parsing, loading, layered resolution, typed access)
- add examples for basic usage and production scenarios

module is deterministic, explicit, and cross-platform