Feat: Re-export every manifest module by one naming rule over the binder's Kotlin names - #21

…der's Kotlin names

The binder serves androidx.compose.* under Kotlin names only and publishes
inspect.signature and python_multiplatform.describe for a Pythonic layer to
read. This is that layer, as one rule in pythonx/compose/_reexport.py: each
module in pythonx-map.toml is a file on disk whose __init__ hands its name to
reexport(), and a name read from it resolves on first use.

- Upper-case names (types, objects, composables) keep their Kotlin spelling;
  every other name is reached by its snake_case spelling only, and an explicit
  overload keeps its suffix. The rule is applied forward to the Kotlin
  module's real names and looked up, never inverted, so toURLString is
  to_url_string and a collision is refused by name.
- Keywords are matched to the declaration's own parameter names from
  describe(), every overload's; an unmatched keyword reaches the binder's own
  refusal unchanged. inspect.signature reports snake_case names and keeps
  KOTLIN_DEFAULT.
- The manifest's raw-primitive allowlist reaches the binder once per
  installed binding layer.
- Names a package defines itself (runtime.Composable) win; resolution is lazy,
  so importing a pythonx.compose module needs no binder.

foundation/, foundation/layout/, ui/text/ and ui/graphics/ get the one-line
__init__ their manifest rows already promised. ui/modifier.py drops the
synthetic-pythonx lookup and reaches Modifier through pythonx.compose.ui.

Methods on a proxy the binder returned (m.fill_max_width()) are the binder's
class's attributes and wait for its member resolver (python-multiplatform
#17, issue #20); the 4 tests that need it skip.

feature added: the re-export rule, the four missing package files.
test added/rewritten: test_chain.py against pythonx (Names 8, Laziness 5,
OverloadDispatch 7, ValueClasses 6, TheChain 6, Handles 1, sources 3),
test_modifier_module.py and test_runtime_module.py import normally.
Red: the new tests against develop, 31 failed, 18 passed, 4 skipped.
Disabling the name rule fails 15, the keyword mapping 1, the allowlist 12.
documentation corrected: SPEC 0/3/S4.1/S5.1/S5.2/S6.x, PROJECT.md, AGENTS.md
section 14, guide status and baseline, three package docstrings.
Suite with ../PythonMultiplatform (develop d00f413f): 44 passed, 33 failed ->
81 passed, 4 skipped. Without a checkout: 40 passed, 37 skipped -> 40 passed,
45 skipped. Each test module run separately passes. check_guide.py: 0.

Refs #8