feat: extract pure fiscal core from sowai-auto (parity-preserving copy)

Copies the 6 pure fiscal modules (domains, chave_acesso, tpag, presets,
resolver, xml_builder) from sowai-auto's backend/app/modules/fiscal/ into
this standalone lib, with only the two mechanical changes required to drop
the app.* dependency: import prefix rename, and TaxRule (ORM) -> TaxRuleLike
(structural Protocol) in the resolver. No other line changes -- byte-level
parity with the auto is the point.

Ports the pure test suites (domains, chave_acesso, resolver with a local
FakeTaxRule satisfying TaxRuleLike, xml_builder) plus a new test_presets_data
covering the PRESETS dict directly (the auto's equivalent test exercises the
apply-preset HTTP/DB flow, which isn't part of the extracted pure core).

55 tests pass locally via `uv run pytest`, no Postgres/k8s required.

pyproject.toml

@@ -0,0 +1,21 @@
+[project]
+name = "sowai-fiscal"
+version = "0.1.0"
+description = "Núcleo fiscal SowAI: motor de regras (imposto-como-dado), chave de acesso, builder de XML NF-e 4.00/NT 2025.002 v1.40"
+requires-python = ">=3.11"
+dependencies = [
+    "pydantic>=2.7",
+    "nfelib>=2.5.2",
+    "lxml>=5.2",
+    "xsdata>=24.0",
+]
+
+[dependency-groups]
+dev = ["pytest>=8", "pytest-asyncio>=0.24"]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["src/sowai_fiscal"]