fix: Fix regex expression of hostname in pydantic v2

[xu-cheng]

The original regex causes errors when loading the generated model.

To Reproduce

Example schema:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Example",
  "type": "object",
  "properties": {
    "data": {
      "type": "string",
      "format": "hostname"
    }
  }
}

Used commandline:

$ datamodel-codegen --output-model-type pydantic_v2.BaseModel --input schema.json --output model.py
$ python3 -m model

Output:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/private/tmp/test/model.py", line 12, in <module>
    class Example(BaseModel):
  File "/private/tmp/test/env/lib/python3.11/site-packages/pydantic/_internal/_model_construction.py", line 174, in __new__
    complete_model_class(
  File "/private/tmp/test/env/lib/python3.11/site-packages/pydantic/_internal/_model_construction.py", line 449, in complete_model_class
    cls.__pydantic_validator__ = SchemaValidator(simplified_core_schema, core_config)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.SchemaError: Error building "model" validator:
  SchemaError: Error building "model-fields" validator:
  SchemaError: Field "data":
  SchemaError: Error building "default" validator:
  SchemaError: Error building "nullable" validator:
  SchemaError: Error building "str" validator:
  SchemaError: regex parse error:
    ^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]{0,61}[A-Za-z0-9])\Z
                                                                                                                        ^^
error: unrecognized escape sequence

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e9b6edf) 100.00% compared to head (e5e1a32) 100.00%.
Report is 676 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #1449     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files           11        32     +21     
  Lines         1020      3556   +2536     
  Branches       201       834    +633     
===========================================
+ Hits          1020      3556   +2536     

Flag	Coverage Δ
unittests	99.63% <99.58%> (?)

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Files Changed	Coverage Δ
datamodel_code_generator/__init__.py	100.00% <100.00%> (ø)
datamodel_code_generator/__main__.py	100.00% <100.00%> (ø)
datamodel_code_generator/format.py	100.00% <100.00%> (ø)
datamodel_code_generator/http.py	100.00% <100.00%> (ø)
datamodel_code_generator/imports.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/__init__.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/base.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/dataclass.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/enum.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/improts.py	100.00% <100.00%> (ø)
... and 22 more

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[koxudaxi]

@xu-cheng
Sorry for the delay in thanking you.
Thank you for your contribution!