feat(i2c): add synchronous slave transmit provider

[floitsch]

Summary

• Correct the 10-bit controller read address sequence.
• Add an ISR-context transmit provider to the I2C target-v2 callbacks, allowing a fixed register map to provide bytes without waiting for an application task.
• Report the transmitted byte count after the transaction so the provider can advance register state safely.

Dependencies

• Builds on fix(i2c): harden slave v2 transactions #121.
• Required by Add register-backed I2C targets toitlang/toit#3155.

Testing

Exercised by Toit's autonomous register-target hardware suite on ESP32 and ESP32-S3, including 7-bit/10-bit addressing, register wrapping, updates, and oversized writes.

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[floitsch]

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Walkthrough

The PR adds synchronous transmit and transmit-completion callbacks to the version-two I2C slave driver. It updates ISR FIFO handling and callback validation. It also corrects 10-bit I2C master read-after-restart address sequencing.

Changes

I2C slave transmit callbacks

Layer / File(s)	Summary
Transmit callback contract components/esp_driver_i2c/include/driver/i2c_types.h, components/esp_driver_i2c/include/driver/i2c_slave.h	The API defines callbacks for supplying synchronous transmit data and reporting transmitted length.
Callback registration and state components/esp_driver_i2c/i2c_private.h, components/esp_driver_i2c/i2c_slave_v2.c	The driver stores transmit callbacks, validates their support and memory location, and rejects i2c_slave_write when a transmit callback is registered.
Transmit FIFO servicing and completion components/esp_driver_i2c/i2c_slave_v2.c	The ISR requests bounded callback data, writes it to the TX FIFO, tracks the byte count, handles completion, and prevents duplicate TX processing.

10-bit I2C master read addressing

Layer / File(s)	Summary
10-bit read address sequencing components/esp_driver_i2c/i2c_master.c	The driver emits the extra address preamble only for the first transaction and writes one byte for the read address.

Estimated code review effort: 3 (Moderate) | ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: adding synchronous slave transmit support for I2C.
Description check	✅ Passed	The description accurately covers the synchronous transmit provider, transmitted-byte reporting, the 10-bit read fix, dependencies, and testing.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch floitsch/i2c-register-provider

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@components/esp_driver_i2c/i2c_private.h`:
- Line 224: Replace tx_data_count in components/esp_driver_i2c/i2c_private.h:224
with state that tracks callback-origin bytes still pending in the FIFO. Update
FIFO loading in components/esp_driver_i2c/i2c_slave_v2.c:73-92 to account
separately for callback and ring-buffer data, and update transmitted calculation
at lines 126-133 to count only callback bytes consumed. At lines 575-576,
serialize callback-mode transitions with pending TX state or preserve source
accounting for already queued data.

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ℹ️ Review info

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Configuration used: Organization UI

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Run ID: e3e64984-9bc2-46fb-b503-b4be14c11b85

📥 Commits

Reviewing files that changed from the base of the PR and between 2fda6ba and e589619.

📒 Files selected for processing (5)

• components/esp_driver_i2c/i2c_master.c
• components/esp_driver_i2c/i2c_private.h
• components/esp_driver_i2c/i2c_slave_v2.c
• components/esp_driver_i2c/include/driver/i2c_slave.h
• components/esp_driver_i2c/include/driver/i2c_types.h