Add recommendation for "escaping" quoted inline script metadata

Issue Description

As described in https://github.com/astral-sh/uv/issues/12303, inline script metadata added naively to a multi-line string will be incorrectly detected as being actual inline script metadata when parsed in accordance with PEP 723 (since the parsing rules are written to be compatible with a basic regex instead of requiring a full Python parser).

https://packaging.python.org/en/latest/specifications/inline-script-metadata/#recommendations should note the problem, and suggest ways to use Python's string quoting flexibility to avoid the misfire.

For example, replacing:

SOURCE_CODE = """
# /// script
# dependencies = ["pydantic", "email-validator"]
# ///
import pydantic

class Model(pydantic.BaseModel):
    email: pydantic.EmailStr

print(Model(email='hello@pydantic.dev'))
"""

with the following compile time string concatenation:

SOURCE_CODE = ("""
"""
"# /// script"
"""
# dependencies = ["pydantic", "email-validator"]
# ///
import pydantic

class Model(pydantic.BaseModel):
    email: pydantic.EmailStr

print(Model(email='hello@pydantic.dev'))
""")

Code of Conduct

• I am aware that participants in this repository must follow the PSF Code of Conduct.

Open the inline script metadata recommendations at packaging.python.org and review the guidance around embedding metadata in Python strings. Add a warning about quoted multiline strings being detected as metadata, include the string-concatenation approach shown in the issue, and confirm the recommendation is clear and accurate.