feat: add board-specific diving stroke codes (F/G/H)

[fsalum]

Hy-Tek writes F, G, and H in the stroke column for diving events. Stroke has no members for them, so select_from_enum falls back to Stroke.UNKNOWN.

That makes diving indistinguishable from file corruption: UNKNOWN is the catch-all for any unrecognized byte, so a consumer cannot tell "this event is diving" from "this file is damaged" — and the two demand opposite handling. Keying diving detection on UNKNOWN silently mislabels corrupt rows as dives; skipping UNKNOWN to be safe silently discards all diving.

The three chars encode the board:

DIVING_1M       = "F"   # 1-metre springboard
DIVING_3M       = "G"   # 3-metre springboard
DIVING_PLATFORM = "H"   # platform

Evidence

From a multi-conference corpus of hy3 files:

• Across 13 multi-diving-event files the chars nest strictly — 8 files carry F+G, 4 carry F+G+H. Never G without F; never H without G.
• Per-file counts line up as parallel events: F=26 G=26 H=26, F=60 G=60 H=54, F=15 G=15 H=12.
• All three carry the same dive count in the distance column within a meet (6 and 11 respectively), so all three are diving rather than some other event type.
• Median scores ascend F < G < H (276.9 / 324.75 / 329.75 and 281.33 / 316.5 / 397.55), matching increasing degree of difficulty from 1-metre to 3-metre to platform.
• High-school meets emit only F, consistent with NFHS rules being 1-metre springboard only.

Verification

select_from_enum(Stroke, "F") is Stroke.DIVING_1M
select_from_enum(Stroke, "G") is Stroke.DIVING_3M
select_from_enum(Stroke, "H") is Stroke.DIVING_PLATFORM
select_from_enum(Stroke, "A") is Stroke.FREESTYLE     # unchanged
select_from_enum(Stroke, "Z") is Stroke.UNKNOWN       # unchanged

Purely additive — no existing member's value changes, so no current behaviour shifts except that F/G/H stop being reported as unknown. The existing test suite passes.

On the omitted numeric aliases

Other members carry ("A", "1", 1) style triples. These three deliberately do not.

Extrapolating 6/7/8 for diving is unverified: no file in the corpus was observed writing a numeric stroke code for a diving event, and a wrong alias would silently mis-map some other numeric code onto diving. select_from_enum(Stroke, …) is only ever called with a single stroke-column character (extract(line, 22, 1)), so the character form is sufficient. Happy to add the numeric forms if you can confirm what Hy-Tek actually writes there.

Note for downstream consumers

For a diving event Hy-Tek puts the dive count (11 for championship format, 6 for dual) in the distance column, and the judged score in the time field. Neither means what its name suggests — a dive score parsed as a time will sort backwards, since higher is better.