fix(python): keep original F# field names in record reflection

[dbrattli]

Problem

Python is the only Fable target that mangles record field names in the reflection TypeInfo, not just the runtime slots. For type Rec = { FirstName: string; HTTPStatus: int; ID: int }:

Backend	FSharpType.GetRecordFields(t).[i].Name
.NET / Fable JS/TS / Fable Beam	FirstName, HTTPStatus, ID
Fable Python (before)	first_name, httpstatus, id

The transform is lossy (httpstatus could be HttpStatus/HTTPStatus/Httpstatus), so any reflection-driven serializer on Python can't reproduce the wire format that .NET and the JS/TS backend produce. Beam already demonstrates the intended design: snake_case runtime map keys, but a pristine F# name in the reflection metadata (name/erl_name split).

Fix

• Compiler (Fable2Python.Reflection.fs): emit fi.Name (pristine) as the reflection field name, adding the snake_case slot as an optional 3rd tuple element, only when it differs from the F# name.
• Runtime (fable-library-py/reflection.py): widen FieldInfo to tuple[str, TypeInfo] | tuple[str, TypeInfo, str]; get_value / get_record_field resolve the attribute via a new _field_attr_name helper (element 2 if present, else 0). Backward-compatible with already-published 2-tuple output.
• Union reflection already kept the pristine name — this brings records in line.

Tests

• Collapsed the #if FABLE_COMPILER fork in TestReflection.fs that enshrined the mangled names ("string"/"int", map [(age..)]) down to the single .NET-matching version.
• Added test Record reflection keeps original F# field names covering { FirstName; HTTPStatus; ID }: reflected names equal the F# names, and GetValue/MakeRecord still resolve the mangled slots.

All 2418 Python tests pass; Pyright clean (0 errors, no # type: ignore).

Notes

src/fable-library-py is PyPI-distributed; this is backward-compatible within the minor version — the library still reads old 2-tuple reflection output, and PropertyInfo.Name semantics only become more correct.

🤖 Generated with Claude Code

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	34
Files with errors	4
Excluded files	4
New errors	✅ No

Excluded files with errors (4 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_hash_set.py	18	Excluded
temp/tests/Python/test_applicative.py	12	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	2	Excluded