fix: exclude python-bindings from coverage build

The Code Coverage job (cargo tarpaulin, nightly toolchain) was failing
to link with:

  rust-lld: error: undefined symbol: _PyEval_RequestCodeExtraIndex
  referenced by pyo3_ffi::cpython::ceval

tarpaulin.toml set `all-features = true`, which enables the optional
`python-bindings` feature and compiles src/python.rs into the coverage
test binary, link-binding libpython. Under the nightly toolchain's
rust-lld (now the default linker) the private CPython symbol does not
resolve, so the binary fails to link. This is deterministic, not a
flake — re-running the job reproduces it.

The bindings are a thin PyO3 FFI shim that cannot be exercised from Rust
tests (they need a live interpreter), so src/python.rs always scored
0/36 lines and contributed nothing measurable. The real Python surface
is covered by the maturin-built pytest suite.

Set `all-features = false` so coverage builds the default feature set.
This drops the unlinkable FFI shim from the build graph and, by removing
36 uncoverable lines from the denominator, nudges reported coverage up
(80.85% -> 81.71% locally) rather than down.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: berisher

tarpaulin.toml

@@ -26,8 +26,15 @@ exclude-files = [
     "benches/*",
 ]
 
-# Run tests with all features
-all-features = true
+# Coverage measures the Rust library and CLI under the default feature
+# set. The optional `python-bindings` feature is deliberately excluded:
+# src/python.rs is a thin PyO3 FFI shim that cannot be exercised from
+# Rust tests (it needs a live interpreter, so it always scored 0/36), and
+# building it links libpython into the coverage test binary, which fails
+# to link under the nightly toolchain's rust-lld (undefined symbol
+# _PyEval_RequestCodeExtraIndex). The Python surface is covered by the
+# maturin-built pytest suite instead.
+all-features = false
 
 # Timeout duration for tests to finish
 test-timeout = "2m"