2c80fae4

By: lcnbr <im@lcnbr.ch>

Make DOT input support optional

Keep DOT parsing enabled by default through the dot feature. Consumers that
construct graphs programmatically can disable default features and omit the
DOT parser. Gate the Rust parse module and Python DOT constructors together;
the programmatic Python Graph and Sampler APIs remain available.

Validation: default library and triangle tests pass (35 tests), as do the
no-default library and triangle tests (34 tests). Benchmarks compile, and
Python API checks pass with and without DOT on Python 3.13. Dependency trees
confirm no dot-parser in either no-default configuration.