Cargo.toml,README.md: Bump version to 0.4.0

[qmonnet]

Main features since v0.3.0 include:

• Support for eBPF-to-eBPF function calls with automatic stack frame management, including:

  • stack frame context preservation during function calls
  • maximum nesting level of 8 function calls
  • customizable StackUsageCalculator for stack size optimization
  • support in both interpreter and JIT modes
  • assembler and disassembler support for eBPF call instructions

• JIT support in no_std mode - users can now manually provide executable memory areas to use JIT without requiring the standard library.

• Replacing single-byte address representation with Range type for memory access ranges, to reduce memory overhead for maps storing large amounts of data; and using the hashbrown crate for better HashMap performance in no_std mode.

• Reduced dependency on libc, obtained by replacing several calls with standard library alternatives:

  • Replaced rand() with a simple Wyrand implementation
  • Replaced libc::memcpy with ptr::copy_nonoverlapping
  • Replaced libc memory allocation with std::alloc
    Only mprotect() remains as a libc dependency.

• Bumping cargo edition to 2024

• Dependency updates, including:

  • replacing the deprecated time v0.2 crate with std::time::Instant, providing cross-platform monotonic time functionality using only the standard library
  • cranelift
  • elf (we were stuck with a very old version because newer versions had breaking changes; these changes have now been addressed)

• Various fixes and clean-ups

(These notes were mostly generated from the Git history by Claude Code.)