fix: use utf-8 for redirect pyproject generation

[Ghraven]

Problem

burr-redirect/generate_pyproject.py reads the template and writes the generated redirect package pyproject.toml without specifying a text encoding. On systems where the preferred locale is not UTF-8, that can make this release helper dependent on the local default encoding.

Before / after

Before, Path.read_text() and Path.write_text() used the platform default encoding.

After, both template read and generated TOML write explicitly use UTF-8, matching the expected encoding for project metadata files.

Verification

• python -m py_compile burr-redirect\generate_pyproject.py
• python burr-redirect\generate_pyproject.py 0.43.0
• Confirmed the generated burr-redirect/pyproject.toml did not change.