feat(fuzz): add cargo-fuzz harness for insert/get/remove sequences

[saiteja00743]

Closes #7

Adds a complete cargo-fuzz setup with a tagged-operation stream harness that exercises PulseMap's core unsafe code paths:

• fuzz/Cargo.toml — fuzz workspace crate (libfuzzer-sys + pulse_map)
• fuzz/rust-toolchain.toml — auto-selects nightly when inside fuzz/
• fuzz/fuzz_targets/fuzz_sequences.rs — fuzz target covering:
  • insert(key, value)
  • get(key) — value integrity check after insert
  • remove(key) — get() == None invariant enforced
  • peek(key) — must agree with get() on presence
  • insert_ttl(key, value, ttl) — per-entry TTL override
  • AdvanceEpoch — dummy inserts to trigger lazy TTL eviction
• fuzz/README.md — setup instructions for Linux, WSL2 (Windows),
  Docker, corpus seeding, crash reproduction,
  and GitHub Actions CI integration

Root Cargo.toml gains [workspace] so cargo check --workspace covers the fuzz crate on stable/Windows without needing nightly.

Invariants checked on every operation:

• get() after remove() always returns None
• get() after insert(k,v) returns the exact same bytes
• peek() and get() always agree on key presence
• len() <= capacity() at all times
• load_factor() stays in [0.0, 1.0]

[ddsha441981]

Hi @saiteja00743 , thanks for jumping on this so quickly! This looks awesome. I'm a bit tied up with my primary work this week, but I will do a detailed review and merge this over the weekend. Appreciate the contribution