…payloads

**Which issue(s) this PR fixes**:
Fixes #

**What this PR does / why we need it**:
This PR introduces a strict upper bound for decompressed payloads.

### Changes

1. Introduced `Fluent::Plugin::Extractor`
   * Extracted the decompression logic (gzip, zstd, deflate) into a dedicated module that processes and decompresses data in manageable 64KB chunks, ensuring steady memory usage.
2. Added `decompression_size_limit` parameter (default: `256MiB`)
   * Specifies the upper limit of decompression in `buffer` (`buf_file`, `buf_file_single` and `buf_memory`) and `in_http` plugins.
   * If the limit is exceeded, it safely raises `Fluent::Plugin::Extractor::SizeLimitError` (or returns a `400 Bad Request` in `in_http`).

### Notice for 3rd-party Plugin Developers
Plugins utilizing the `buffer` / `in_http` mechanisms or the newly introduced `Fluent::Plugin::Extractor` are automatically protected by this limit.

However, if your custom plugin implements its own decompression logic independently, you must take care to implement similar boundary checks to guard against unexpected memory spikes.

**Docs Changes**:

**Release Note**:
* buffer, in_http: enforce size limits on decompressed payloads

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>