refactor: remove unused MaybeString wrapper type (#336)

## Summary
- Delete `MaybeString` newtype wrapper
(`crates/vite_task/src/maybe_str.rs`)
- It existed solely to add bincode `Encode`/`Decode` to `Vec<u8>`, which
wincode supports natively
- The type was never referenced outside its own module

## Test plan
- [x] `cargo clippy` passes
- [x] `cargo test --workspace --exclude fspy` passes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: branchseer

Cargo.lock

@@ -15,7 +15,6 @@ workspace = true
 anyhow = { workspace = true }
 async-trait = { workspace = true }
 wincode = { workspace = true, features = ["derive"] }
-bstr = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
 ctrlc = { workspace = true }
 derive_more = { workspace = true, features = ["from"] }

crates/vite_task/Cargo.toml

@@ -1,6 +1,5 @@
 mod cli;
 mod collections;
-mod maybe_str;
 pub mod session;
 
 // Public exports for vite_task_bin