[Bug] REST catalog drop_table serializes purgeRequested as "True" instead of "true"

### Apache Iceberg version

None

### Please describe the bug 🐞

### Description

`RestCatalog.drop_table()` passes a Python `bool` directly to `requests` query params. Python's `requests` library
serializes `True` as the string `"True"` (capitalized). This violates the OpenAPI 3.0 specification for boolean
query parameters and causes 400 errors on spec-compliant servers.

### Steps to Reproduce

```python
from pyiceberg.catalog import load_catalog

catalog = load_catalog("my_catalog", **{
"type": "rest",
"uri": "http://my-rest-catalog/iceberg",
...
})

catalog.drop_table("my_db.my_table", purge_requested=True)
# → 400 Bad Request
Evidence

Enabled wire-level logging via http.client.HTTPConnection.debuglevel = 1:
send: b'DELETE /iceberg/v1//namespaces/my_db/tables/my_table?purgeRequested=True HTTP/1.1\r\n...'

reply: 'HTTP/1.1 400 Bad Request\r\n'
header: x-amzn-errortype: purge_enabled
body: {"error":{"type":"BadRequestException","message":"purge_enabled: DropTable operation failed. OSS Tables only
supports dropping tables with purge enabled."}}
The server receives purgeRequested=True (capital T) and does not interpret it as boolean true.

Root Cause

pyiceberg/catalog/rest/__init__.py, drop_table method (~line 1135):
def drop_table(self, identifier: str | Identifier, purge_requested: bool = False) -> None:
response = self._session.delete(
self.url(Endpoints.drop_table, prefixed=True, **self._split_identifier_for_path(identifier)),
params={"purgeRequested": purge_requested}, # Python bool True → requests serializes as "True"
)
Python's requests library calls str() on param values: str(True) → "True".

Why This Is a Bug

The Iceberg REST catalog OpenAPI spec (rest-catalog-open-api.yaml
(https://github.com/apache/iceberg/blob/main/open-api/rest-catalog-open-api.yaml)) defines purgeRequested as:
- name: purgeRequested
in: query
schema:
type: boolean
Per the specification chain:

- OpenAPI 3.0.3, Parameter Object (https://spec.openapis.org/oas/v3.0.3#parameter-object): query parameters default
to style: form; primitive types are based on "JSON Schema Specification Wright Draft 00"
- JSON Schema Wright Draft 00, Section 4.1
(https://datatracker.ietf.org/doc/html/draft-wright-json-schema-validation-00#section-4.1): type: boolean accepts
only JSON boolean literals
- RFC 7159 (The JSON Data Interchange Format), Section 3 (https://datatracker.ietf.org/doc/html/rfc7159#section-3):
the only boolean literals are true and false (lowercase)

"True" (capitalized) is not a valid serialization of a JSON boolean.

Suggested Fix
params={"purgeRequested": str(purge_requested).lower()},
Or more explicitly:
params={"purgeRequested": "true" if purge_requested else "false"},
Scope

This pattern may exist elsewhere in the REST catalog client. A grep for params={ in
pyiceberg/catalog/rest/__init__.py would identify other occurrences where Python bools are passed as query
parameters.

Environment

- PyIceberg: 0.11.1
- Python: 3.10.21
- Server: Aliyun OSS Tables (Iceberg REST compatible, strictly validates boolean query params)
- requests: 2.x (serializes bool via str())

### Willingness to contribute

- [x] I can contribute a fix for this bug independently
- [ ] I would be willing to contribute a fix for this bug with guidance from the Iceberg community
- [ ] I cannot contribute a fix for this bug at this time

从 pyiceberg/catalog/rest/__init__.py 中的 RestCatalog.drop_table 开始，检查 issue 中建议的其他 params= 出现位置。复现该请求或运行相关的 REST catalog 检查，然后验证 purgeRequested 是否被序列化为小写的 true 或 false，并确认服务器接受它。

由索引模型根据 Issue 内容生成。