feat(beam): dual-API bindings — BeamChardata, io_lib, and raw-list variants

[dbrattli]

Follow-up to #123. Establishes a dual-API convention for bindings whose OTP function returns a
BEAM-native form (chardata, or a raw Erlang list) that is efficient for authoring Erlang but awkward
in idiomatic F#, and applies it across the library.

The convention (written up in BINDINGS-GUIDE.md): bind such a function twice — an F#-friendly
default under the plain name (a flattened string, or a ref-wrapped 'T array), and a <name>Raw
variant returning the BEAM-native type (BeamChardata or BeamList<'T>) for zero-copy output and
interop with hand-written Erlang.

BeamChardata

An erased unicode:chardata(), in the BeamList/BeamMap family (Types.fs):

[<Erase>] type BeamChardata = BeamChardata of obj
BeamChardata.ofString : string -> BeamChardata   // a binary is already valid chardata (zero cost)
BeamChardata.toString : BeamChardata -> string   // flatten via unicode:characters_to_binary

Not BeamList<char>, as first sketched: only reverse yields a charlist; pad/replace yield
iodata (nested binaries and integers), which BeamList<char> would misrepresent. One honest chardata
type covers all of them.

What's bound dual-API

Native form	Default (F#)	*Raw (BEAM)	Functions
chardata	string	BeamChardata	string:reverse/pad/padDir/padWith/replaceFirst/replaceAll, uri_string:compose_query, io_lib:format (new)
raw list	'T array	BeamList<'T>	maps:keys/values/to_list, string:split×2, binary:split×2, re:split×4, proplists:get_keys

io_lib is a new module (IoLib.fs) — io_lib:format is the canonical build-a-string-from-a-template
function and returns chardata, so it gets format (→ string) + formatRaw (→ BeamChardata).

The existing default bindings are unchanged; every *Raw is additive.

Also fixes (from #123's aftermath)

Supersedes the commented-out reverse/pad ImportAll stubs: they returned chardata and never could
be ImportAll members, but are fully bound now (string + raw), so the stubs became one-line pointers.

Small structural change

BeamList (in Lists.fs) was compiled after Maps.fs, so Maps couldn't reference it. Lists and
Maps are mutually independent, so Lists.fs now compiles first and Maps.fs opens it (as do
String.fs/Re.fs).

Verification

just test    # 380 passed, 0 failed  (+13: raw round-trips, native-form equality, io_lib)
just spike   # 11 passed, exit 0

Every *Raw list test asserts the native form matches its array member (length / structural
equality); every chardata *Raw test asserts an isList proof it's unflattened plus a
toString round-trip back to the default.

🤖 Generated with Claude Code