feat: expand bounded TensorFlow CPU unary and BiasAdd surface

[rextio]

Summary

• add rank-1 float32 CPU tf.nn.softmax for omitted final axis or literal positional/keyword axis=0, while preserving the existing rank-2 explicit axis=1 contract
• add exact rank-1/rank-2 float32 CPU tf.abs, tf.negative, tf.square, tf.exp, tf.math.log, and tf.math.sqrt lowering through owned TFE unary operations
• add bounded tf.nn.bias_add for rank-2 value plus rank-1 bias with data format omitted or literal NHWC
• keep tf.maximum and tf.minimum unclaimed until the full broadcast, incompatible-shape, NaN/Inf, and signed-zero matrix is certified across native profiles

Contract and safety

• retains CPython 3.11, TensorFlow 2.21.0, plugin API 1.3, float32 CPU rank-1/rank-2, and inference-only boundaries
• preserves exact eager-context reuse, RAII tensor/op ownership, CPU device checks, and result rank/dtype validation
• resolves the sole new ABI symbol, TFE_OpSetAttrString, through the existing RTLD_NOLOAD handle and dladdr owning-image provenance check before setting data_format=NHWC
• rejects NCHW, dynamic or forged metadata, keyword tensor operands, unsupported aliases, wrong rank/order/dtype/device, receivers, and extra options
• does not change Core, LSP, VS Code, CUDA, WASM, training behavior, package pins, platform support, or release state

Verification

• pytest tests -m "not needs_cargo" -q: 305 passed, 1 skipped
• ruff check src tests: passed
• mypy src: passed
• real-Cargo E2E coverage was expanded for all accepted forms, special values, shape/dtype/rank errors, symbol provenance, and lifetime behavior; the module collects all five tests
• native Cargo execution was not run locally because this host does not have the required CPython 3.11 + TensorFlow 2.21 environment; the blocking macOS arm64 and Linux x86_64 CI jobs remain authoritative

Commit structure

1. 0d86e8d — rank-1 Softmax
2. 4550d24 — bounded math unary operations
3. 6042222 — bounded NHWC BiasAdd and explicit Maximum/Minimum defer

Release disposition

This PR targets the unreleased 0.1.2 integration branch. It does not authorize merge, tag creation, package publication, or release.