Niquests

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**Added**
- "Repr" for our HTTPAdapter and AsyncHTTPAdapter for debugging purposes. (201) (227)
- Top level `aget`, `apost`, `aput`, ..., as the asynchronous counterpart of `niquests.get`, `niquests.post`, ...
- Global timeout configuration per `Session` or `AsyncSession`. Like `Session(timeout=10)`. (232)
- `iter_raw` method in `Response` and `AsyncResponse` in order to retrieve content from remote without decompression. (233)

**Fixed**
- Missing awaited coroutine in `AsyncResponse.close(...)`. (231)
- Attempt to call `close` coroutine (urllib3 raw Response) in async mode when the response is not awaitable.

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**Added**
- Internal shortcut to urllib3-future as `niquests.packages.urllib3`. This immediately helps end-user migrating
from Requests to Niquests and avoid the confusion around `urllib3` and `urllib3-future`.
The package own code benefit from it. `idna`, `charset_normalizer` (+ aliased as `chardet`) can be used also.

**Misc**
- The documentation is improved. Especially around sync/async examples and migration snippets.

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**Removed**
- Dependency on `idna`. Since qh3 version 1.4, we can rely on their internal idna encoder that does not require any external dependencies.
This change does not affect the feature on international domain names. If `idna` is installed, it will be used instead.
- Dependency on `kiss-headers`. We decided to vendor kiss-headers into Niquests for several reasons. The principal one
is that the project is stable and require next to no maintenance. And pulling extra dependencies affect some end-users.
We are in the process of measuring potential interest for kiss-headers models. We may decide to remove its support completely
in a next major version.

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**Changed**
- Relaxed strict compliance on JSON parsing. We brought strict compliance into Niquests, a response
must explicitly set `Content-Type: application/json` or alike prior to attempt parsing the JSON string.
We decided to relax that constraint as old and bad-behaving server may send JSON with missing or broken Content-Type.

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**Fixed**
- Parsing of special scheme that exceed 9 characters on rare custom adapters.

**Changed**
- Default `Content-Type` for json payloads changed from `application/json; charset="utf-8"` to `application/json;charset=utf-8`.
While the previous default was valid, this is the preferred value according to RFC9110. (204)

**Misc**
- Removed a useless hasattr control to support older version of urllib3-future (<2.5).
- Updated our pre-commit configuration and reformatted files accordingly.

-------------------

**Fixed**
- Certificate validation may end up in error in highly concurrent environment using the experimental freethreaded build.
This was due to a racing condition in our "verify" caching logic (e.g. avoid creating duplicate ssl_context where one is sufficient).
The GIL prevented this issue.