Add Q, R, C, and GF2 fields

- add `lalib.fields.base.Field`, a blueprint for all concrete fields,
  providing a unified interface to be used outside of the
  `lalib.fields` sub-package
- implement `lalib.fields.complex_.ComplexField`, or `C` for short,
  the field over the complex numbers (modeled as `complex` numbers)
- implement `lalib.fields.galois.GaloisField2`, or `GF2` for short,
  the (finite) field over the two elements `one` and `zero`
  + adapt `lalib.elements.galois.GF2Element.__eq__()` to return
    `NotImplemented` instead of `False` for non-castable `other`s
    => this fixes a minor issue with `pytest.approx()`
- implement `lalib.fields.rational.RationalField`, or `Q` for short,
  the field over the rational numbers (modeled as `fractions.Fraction`s)
- implement `lalib.fields.real.RealField`, or `R` for short,
  the field over the real numbers (modeled as `float`s)
- organize top-level imports for `lalib.fields`,
  making `Q`, `R`, `C`, and `GF2` importable with
  `from lalib.fields import *`
- provide extensive unit and integration tests for the new objects:
  + test generic and common behavior in `tests.fields.test_base`
  + test specific behavior is other modules
  + test the well-known math axioms for all fields (integration tests)
  + test the new objects' docstrings
  + add "pytest-repeat" to run randomized tests many times

poetry.lock

@@ -1234,6 +1234,20 @@ files = [
 importlib-metadata = {version = ">=3.6.0", markers = "python_version < \"3.10\""}
 pytest = "*"
 
+[[package]]
+name = "pytest-repeat"
+version = "0.9.3"
+description = "pytest plugin for repeating tests"
+optional = false
+python-versions = ">=3.7"
+files = [
+    {file = "pytest_repeat-0.9.3-py3-none-any.whl", hash = "sha256:26ab2df18226af9d5ce441c858f273121e92ff55f5bb311d25755b8d7abdd8ed"},
+    {file = "pytest_repeat-0.9.3.tar.gz", hash = "sha256:ffd3836dfcd67bb270bec648b330e20be37d2966448c4148c4092d1e8aba8185"},
+]
+
+[package.dependencies]
+pytest = "*"
+
 [[package]]
 name = "pyyaml"
 version = "6.0.2"
@@ -1714,4 +1728,4 @@ type = ["pytest-mypy"]
 [metadata]
 lock-version = "2.0"
 python-versions = "^3.9"
-content-hash = "31a7b1ad8dd8949814d1f397022e400cd37643c6f5e9e438054de472091bcd69"
+content-hash = "a10f3c13ed0c67e6ea65500335281cd269e3efdd0fae544ad667d07637ef118f"