[lvgl] Add radial and conical gradient support

[Copilot]

What does this implement/fix?

LVGL 9.5.0 added support for radial and conical gradient types via lv_grad_radial_init(), lv_grad_radial_set_focal(), and lv_grad_conical_init(). This PR adds the necessary ESPHome Python configuration code to expose these new gradient types, alongside a new LV_GRAD_EXTEND constant (PAD/REPEAT/REFLECT) used by all three positional gradient types (linear, radial, conical).

The existing HOR/VER gradient handling is unchanged. The new LINEAR type exposes the full lv_grad_linear_init() API (previously only accessible via the HOR/VER shortcuts).

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected) — policy
• Developer breaking change (an API change that could break external components) — policy
• Undocumented C++ API change (removal or change of undocumented public methods that lambda users may depend on) — policy
• Code quality improvements to existing code or addition of tests
• Other

Related issue or feature (if applicable):

Pull request in esphome-docs with documentation (if applicable):

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040/RP2350
• BK72xx
• RTL87xx
• LN882x
• nRF52840

Example entry for config.yaml:

lvgl:
  gradients:
    # Linear gradient with custom start/end points and extend mode
    - id: diagonal_grad
      direction: LINEAR
      linear:
        from_x: 0%
        from_y: 0%
        to_x: 100%
        to_y: 100%
        extend: PAD
      stops:
        - color: 0xFF0000
          position: 0
        - color: 0x0000FF
          position: 255

    # Radial gradient (circle expanding from center)
    - id: radial_grad
      direction: RADIAL
      radial:
        center_x: 50%
        center_y: 50%
        to_x: 100%
        to_y: 50%
        extend: PAD
      stops:
        - color: 0xFFFFFF
          position: 0
        - color: 0x000000
          position: 255

    # Radial gradient with a focal point (offset inner circle)
    - id: radial_focal_grad
      direction: RADIAL
      radial:
        center_x: 50%
        center_y: 50%
        to_x: 100%
        to_y: 50%
        focal_x: 30%
        focal_y: 40%
        focal_radius: 10
        extend: REPEAT
      stops:
        - color: 0xFF8800
          position: 0
        - color: 0x0088FF
          position: 255

    # Conical gradient (angular sweep around a center point)
    - id: conical_grad
      direction: CONICAL
      conical:
        center_x: 50%
        center_y: 50%
        start_angle: 0
        end_angle: 360
        extend: PAD
      stops:
        - color: 0xFF0000
          position: 0
        - color: 0x00FF00
          position: 127
        - color: 0xFF0000
          position: 255

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[github-actions]

To use the changes from this PR as an external component, add the following to your ESPHome configuration YAML file:

external_components:
  - source: github://clydebarrow/esphome@pull/143/head
    components: [lvgl]
    refresh: 1h

---

(Added by the PR bot)

[github-actions]

Memory Impact Analysis

Components: lvgl
Platform: esp32-idf

Metric	Target Branch	This PR	Change
RAM	56,284 bytes	56,660 bytes	📈 🔸 +376 bytes (+0.67%)
Flash	1,259,903 bytes	1,261,107 bytes	📈 🔸 +1,204 bytes (+0.10%)

📊 Component Memory Breakdown

Component	Target Flash	PR Flash	Change
[esphome]core	118,355 bytes	119,065 bytes	📈 🔸 +710 bytes (+0.60%)
[lib]lvgl	318,750 bytes	319,009 bytes	📈 +259 bytes (+0.08%)
libc	60,419 bytes	60,505 bytes	📈 +86 bytes (+0.14%)
[lib]mdns	25,267 bytes	25,275 bytes	📈 +8 bytes (+0.03%)

🔍 Symbol-Level Changes (click to expand)

Changed Symbols

Symbol	Target Size	PR Size	Change
setup()	26,638 bytes	27,330 bytes	📈 +692 bytes (+2.60%)
mdns_priv_browse_sync	79 bytes	87 bytes	📈 +8 bytes (+10.13%)

New Symbols (top 15)

Symbol	Size
lv_grad_radial_init	78 bytes
esphome__radial_focal_grad__pstorage	76 bytes
esphome__radial_grad__pstorage	76 bytes
esphome__linear_grad__pstorage	76 bytes
esphome__conical_grad__pstorage	76 bytes
lv_grad_conical_init	70 bytes
lv_grad_linear_init	67 bytes
C$1651$8	44 bytes
lv_grad_radial_set_focal	44 bytes
C$1559$6	40 bytes
C$1566$7	40 bytes
C$484$3	28 bytes
setup()::conical_grad_colors_	9 bytes
guard variable for setup()::radial_focal_grad_colors_	8 bytes
guard variable for setup()::linear_grad_colors_	8 bytes
14 more new symbols...	Total: 800 bytes

Removed Symbols (top 15)

Symbol	Size
C$1643$8	44 bytes
C$1551$6	40 bytes
C$1558$7	40 bytes
C$476$3	28 bytes
C$64$2	8 bytes

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Note: This analysis measures static RAM and Flash usage only (compile-time allocation).
Dynamic memory (heap) cannot be measured automatically.
⚠️ You must test this PR on a real device to measure free heap and ensure no runtime memory issues.

This analysis runs automatically when components change. Memory usage is measured from a representative test configuration.