chore: add vendor dependencies for kauma build

vendor/ryu/README.md

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+# Ryū
+
+[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/ryu-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/ryu)
+[<img alt="crates.io" src="https://img.shields.io/crates/v/ryu.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/ryu)
+[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-ryu-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/ryu)
+[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/ryu/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/ryu/actions?query=branch%3Amaster)
+
+Pure Rust implementation of Ryū, an algorithm to quickly convert floating point
+numbers to decimal strings.
+
+The PLDI'18 paper [*Ryū: fast float-to-string conversion*][paper] by Ulf Adams
+includes a complete correctness proof of the algorithm. The paper is available
+under the creative commons CC-BY-SA license.
+
+This Rust implementation is a line-by-line port of Ulf Adams' implementation in
+C, [https://github.com/ulfjack/ryu][upstream].
+
+*Requirements: this crate supports any compiler version back to rustc 1.36; it
+uses nothing from the Rust standard library so is usable from no_std crates.*
+
+[paper]: https://dl.acm.org/citation.cfm?id=3192369
+[upstream]: https://github.com/ulfjack/ryu/tree/77e767f5e056bab96e895072fc21618ecff2f44b
+
+```toml
+[dependencies]
+ryu = "1.0"
+```
+
+<br>
+
+## Example
+
+```rust
+fn main() {
+    let mut buffer = ryu::Buffer::new();
+    let printed = buffer.format(1.234);
+    assert_eq!(printed, "1.234");
+}
+```
+
+<br>
+
+## Performance (lower is better)
+
+![performance](https://raw.githubusercontent.com/dtolnay/ryu/master/performance.png)
+
+You can run upstream's benchmarks with:
+
+```console
+$ git clone https://github.com/ulfjack/ryu c-ryu
+$ cd c-ryu
+$ bazel run -c opt //ryu/benchmark:ryu_benchmark
+```
+
+And the same benchmark against our implementation with:
+
+```console
+$ git clone https://github.com/dtolnay/ryu rust-ryu
+$ cd rust-ryu
+$ cargo run --example upstream_benchmark --release
+```
+
+These benchmarks measure the average time to print a 32-bit float and average
+time to print a 64-bit float, where the inputs are distributed as uniform random
+bit patterns 32 and 64 bits wide.
+
+The upstream C code, the unsafe direct Rust port, and the safe pretty Rust API
+all perform the same, taking around 21 nanoseconds to format a 32-bit float and
+31 nanoseconds to format a 64-bit float.
+
+There is also a Rust-specific benchmark comparing this implementation to the
+standard library which you can run with:
+
+```console
+$ cargo bench
+```
+
+The benchmark shows Ryū approximately 2-5x faster than the standard library
+across a range of f32 and f64 inputs. Measurements are in nanoseconds per
+iteration; smaller is better.
+
+## Formatting
+
+This library tends to produce more human-readable output than the standard
+library's to\_string, which never uses scientific notation. Here are two
+examples:
+
+- *ryu:* 1.23e40, *std:* 12300000000000000000000000000000000000000
+- *ryu:* 1.23e-40, *std:* 0.000000000000000000000000000000000000000123
+
+Both libraries print short decimals such as 0.0000123 without scientific
+notation.
+
+<br>
+
+#### License
+
+<sup>
+Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
+2.0</a> or <a href="LICENSE-BOOST">Boost Software License 1.0</a> at your
+option.
+</sup>
+
+<br>
+
+<sub>
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
+be dual licensed as above, without any additional terms or conditions.
+</sub>