feat(std): establish a portable versioned standard library foundation

[LunaStev]

Summary

This PR completes the current standard-library foundation work and extends it into a portable OS and architecture provider model.

• defines documented public std::fs and std::io APIs with runnable file examples
• makes std updates compatibility-versioned, staged, validated, transactional, and rollback-safe
• separates portable APIs from OS providers and architecture-specific syscall ABIs
• adds Linux amd64, arm64, and riscv64 providers
• adds macOS amd64 and arm64 providers
• adds an initial FreeBSD amd64 provider and compiler target
• adds architecture-neutral Windows Win32 and Winsock providers shared by x86-64 and ARM64
• adds the aarch64-w64-windows-gnu compiler target and extern(system) ARM64 handling
• expands native, cross-target, corpus, example, and CI coverage

Issue coverage

Standard-library layering and contracts

• keeps user-facing modules independent from raw syscall providers
• documents public std and libc surfaces with short usage-oriented comments
• centralizes OS and architecture selection through target attributes
• rejects duplicate target keys and canonicalizes OS and architecture aliases

Version-aware transactional std updates

• adds a standard-library compatibility revision manifest
• rejects incompatible installed std revisions with an actionable diagnostic
• stages and validates the complete Wave source tree before activation
• records installation source metadata
• atomically replaces an installation and restores the previous tree on activation failure
• adds replacement and rollback regression tests with isolated HOME directories

User-facing filesystem API

• adds portable open, create, read, write, append, copy, rename, metadata, directory, and removal helpers
• provides fixed-buffer and growable-buffer read paths
• updates the file I/O example to the public API
• adds end-to-end filesystem coverage

Additional work

• adds FreeBSD target selection, object generation, linker planning, sysroot, and CRT handling
• corrects Linux, Darwin, and FreeBSD termios layouts and syscall contracts
• adds Windows file, environment, memory, process, socket, time, and tty provider surfaces
• maps Windows standard descriptors through GetStdHandle
• keeps Windows std implementations architecture-neutral while retaining architecture-specific LLVM and C ABI target handling
• fixes TypedBuffer pointer arithmetic exposed by the new runtime tests
• verifies ARM64 and x86-64 COFF machine headers independently
• adds 11 Wave E2E cases for string, path, buffer, environment, time, math, and cross-target std object generation
• adds 12 focused examples under examples/std
• runs the std example suite natively on Linux amd64 and arm64, macOS amd64 and arm64, and Windows CI
• limits Cargo CI parallelism to two jobs and applies the same example gate to release validation

Validation

• cargo fmt --all --check
• cargo test --locked --workspace --jobs 2
• RUSTDOCFLAGS=-D warnings cargo doc --locked --no-deps --jobs 2
• standard-library policy validation
• 43 codegen regression tests
• 167 of 167 Wave corpus files
• 12 of 12 standard-library examples
• 113 Wave E2E passes, 8 platform or sandbox skips, 0 failures
• Windows x86-64 and ARM64 COFF object generation
• git diff --check

Closes #375
Closes #379
Closes #380