Build without std, and 0.4.5

[pathscale]

An adaptive radix tree over raw pointers and atomics. Nothing in it needed an operating system, and it linked one anyway — which is what stopped every consumer that wanted to be no_std from being it.

core::   ptr, mem, marker, fmt, hint, cmp, slice, arch, alloc::Layout
alloc::  Arc, Vec, Box, format!, the allocator calls

The two things that genuinely wanted std

• debug_print writes to stdout, so it is behind the feature.
• thread::yield_now in the spin backoff falls back to core::hint::spin_loop() when there is no scheduler to yield to. That is the same instruction the fast path directly above it already executes, minus the syscall.

stats keyed its per-level counters by depth in a HashMap. It is a BTreeMap now — the same map without a hasher, and the one alloc has.

serde and ps-reclaim arrive with default features off and get std back through this crate's own feature, which is default-on, so nothing downstream changes unless it asks.

default                  congee-wt [default,std]  ps-reclaim [libc,spin,std]
--no-default-features    congee-wt []             ps-reclaim [libc,spin]

Doc examples still say std::, deliberately: a doctest compiles as a consumer, and a consumer has one.

What no_std does not mean here

It does not mean bare metal. ps-reclaim keeps its participant slot in thread-local storage and its no_std path is pthread keys, so this still needs an operating system — x86_64-unknown-none stops at ps-reclaim, not at this crate. no_std is a statement about the standard library, not about a class of hardware.

Checks

cargo test                     103 + 7 + 39 passed, 0 failed
clippy, std and no_std         clean
cargo fmt --check              clean

Version 0.4.5. Also carries the house working agreement (AGENTS.md, CLAUDE.md), which was sitting unpushed locally.

Companion to pathscale/WorkTablesIndex (same port) and pathscale/parking_lot_lite_hack#3. worktable-vec is the consumer that wanted both: pathscale/WorkTable-vec#4 currently has to declare that its congee and wti features imply std, and this is half of what removes that.