feat(player): give SpriteStudioPlayer2D real enums and ClassDB properties

[Naruto]

What

Registers the two halves of SpriteStudioPlayer2D's public surface that never reached ClassDB: the enums behind its int parameters, and the inspector properties.

Enums

set_playback_direction, set_part_color_override* and set_part_cell_override took plain ints documented only in a comment. Four enums are added and taken as parameter types, and bound alongside the existing AnimationProcessMode:

enum	constants
AnimationProcessMode	ANIMATION_PROCESS_PHYSICS / _IDLE
PlaybackDirection	PLAYBACK_DIRECTION_FORWARD / _BACKWARD
PlaybackStyle	PLAYBACK_STYLE_NORMAL / _PING_PONG
ColorBlendOperation	COLOR_BLEND_MIX / _MUL / _ADD / _SUB
OverridePriority	OVERRIDE_PRIORITY_NEXT_KEYFRAME / _UNTIL_ANIMATION_CHANGE / _PERMANENT

Values follow the runtime's FFI encoding (ss_runtime_set/get_playback_direction normalizes direction and style to 0/1 on both sides, so these are not the Rust PlaybackDirection discriminants; blend_op and priority_mode match ssruntime.h). DEFVAL now names the default instead of spelling 0 / 1.

Bug fixed along the way: AnimationProcessMode's two constants were already registered via BIND_CONSTANT (constants with no enum). That collided with BIND_ENUM_CONSTANT — Class 'SpriteStudioPlayer2D' already has constant 'ANIMATION_PROCESS_PHYSICS' — and kept the enum out of ClassDB, even though doc_classes/ already described the property as enum="SpriteStudioPlayer2D.AnimationProcessMode". The old binding is dropped.

Properties

Only ssab was registered; the other 17 came from _set / _get / _get_property_list, so they were invisible to ClassDB.class_get_property_list, to the doc tooling, and to any binding generator. They move to ADD_PROPERTY / ADD_GROUP, with the three genuinely instance-dependent hints — the animation name list and the frame / section ranges — injected through _validate_property, the same pattern SpriteStudioPartAttachment2D already uses for part_name.

• cellmaps/* stays in _get_property_list: both its count and its names come from the resource.
• frame_rate / playback_direction / playback_style stay in _set / _get — reachable by name, deliberately absent from the property list, and already covered by bound accessors.
• set_animation_section_start / set_animation_section_end are added because ADD_PROPERTY needs single-argument setters. set_animation_section(start, end) is unchanged.

Compatibility

Names, order, hints and usage flags are unchanged — including frame's editor-only usage — so existing scenes keep loading and the inspector looks the same. GDScript passing raw ints to the now-enum parameters still compiles.

One visible difference: ADD_PROPERTY lets Godot resolve default values, so a re-saved scene omits properties left at their default instead of writing all 17. Verified by packing and saving a scene:

=== all-default player ===
[node name="Player" type="SpriteStudioPlayer2D" parent="." unique_id=2105169513]

=== modified player ===
[node name="Player" type="SpriteStudioPlayer2D" parent="." unique_id=246106748]
speed_scale = 2.0
flip_h = true

Test plan

• ./scripts/build-extension.sh target=editor (macOS arm64) — builds and links
• ./scripts/build.sh target=editor (macOS arm64, custom module) — builds and links
• Headless ClassDB inspection against the module build:
  • all 5 enums appear in class_get_enum_list with the expected constants
  • class_get_property_list reports the 17 properties + 4 groups in the original order, with the original hints and usage flags (frame still PROPERTY_USAGE_EDITOR only)
  • _validate_property injects the live hints: animation → 'Arrow_Attack', frame → '0,70.0,0.01', section → '0,70.0,1'
  • round trip on frame_rate, direction/style, section endpoints, animation_process_mode, and set_part_color_override with default arguments
• doc_classes/SpriteStudioPlayer2D.xml compiles into doc_data.gen.cpp

Runtime behaviour of the GDExtension build was not exercised separately — it shares _bind_methods with the module build, and ADD_GROUP / _validate_property already have working precedent in both builds via SpriteStudioPartAttachment2D.

Docs

doc_classes/SpriteStudioPlayer2D.xml gains the new constants and the two section members; the value tables in docs/{en,ja}/api/player.md and docs/{en,ja}/workflow/usage_scripting.md now name the constants next to the numbers.