Unbounded memory allocation in `evtx` parsing a `.wevtcache` file

Summary

Affected versions of `evtx` did not bound a per-entry payload length read from a `.wevtcache` file before allocating a buffer sized from it, allowing a tiny crafted file to force a multi-gigabyte allocation and abort the process (out-of-memory denial of service, CWE-400).

## Details

In `WevtCacheReader::next_entry` (`src/wevt_templates/wevtcache.rs`), the per-entry payload length is read as a `u64` straight from the file and used to size a zeroing buffer **before** any data is read:

```rust let len = usize::try_from(len_u64)?; // u64 taken directly from the entry header let mut buf = vec![0u8; len]; // unbounded allocation, sized from the file reader.read_exact(&mut buf)?; // only fails AFTER the allocation ```

The only check on `len` is that it fits in `usize`; there is no check that it fits within the bytes remaining in the file. An entry header declaring a ~4 GiB length therefore makes the crate request a ~4 GiB allocation from a file of only ~25 bytes.

The sink is reachable through the public API `evtx::wevt_templates::wevtcache::for_each_crim_blob(path, f)` (and the `WevtCacheReader::next_entry` it drives). The `.wevtcache` reader first shipped in `0.11.0`, and every published version from `0.11.0` through `0.14.0` is affected. The code lives in the `wevt_templates` feature, which is enabled by default through the `evtx_dump` feature. The fix landed in `0.15.1`: `0.15.0` was tagged but never published to crates.io (its Windows build failed), so `0.15.1` is the first patched release available. The Python bindings (`evtx` on PyPI) carry the fix as of `0.15.0`.

## Reproduction

A ~25-byte file is sufficient: the `.wevtcache` magic (`WEVTCACH`), a `version` (u32 LE) of `1`, an `entry_count` (u32 LE) of `1`, then one entry consisting of a `kind` byte and a `len` (u64 LE) set to a large value (e.g. `0xFFFFFFF0`), with no payload bytes following. Passing that file to `for_each_crim_blob` triggers the oversized allocation before the short read fails.