Update lint and test Github workflows; add Python 3.13 and 3.14 tests

[davidpirogov]

Description

Added Python 3.13 and 3.14 tests to Github Actions.

Added more restrictive permissions to the Github Workflows to ensure that we're only giving limited permissions to actions. (No effective change to current Github Workflows, just makes them more secure)

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

[davidpirogov]

Failing 3.8 tests will be fixed once PR #24 is approved and merged. (expected failure)

[Justar96]

@davidpirogov and let's wait for #24 to be merged first
These should be in [dependency-groups.dev]

• Runtime deps should be minimal (dev tool, not runtime dependency)

[dependency-groups]
benchmark = ["tiktoken>=0.4.0"]
dev = [
    "pytest>=8.0.0",
    "pytest-cov>=4.1.0",
    "ruff>=0.8.0",
    "mypy>=1.8.0",
]