Bugfix/improve event handling path timing

[alisitsyn]

Description

This MR addresses the throughput issues in Modbus TCP Slave. The investigation of timing aspects in the loop is performed as part of this PR. The event loop has been improved to decrease gap time between reading of different registers when more events (IO + sock events) are happened with multi-master connections. Different events can be processed sequentially avoiding additional time gaps with the select() timeouts. Additional kconfig values are added for fine tune of the TCP event loop processing.

Related

Fixes: EPROT-50
Related: EPROT-55

Testing

The testing is performed manually with four masters connected to the same ESP32 Modbus TCP Slave. The event loop related parameters and their impact to overall processing are investigated and moved to kconfig configuration allowing better turning in user applications.

Kconfig Option	Default	Range	Macro	Impact
FMB_TCP_SELECT_WAIT_MS	50	10–500	MB_SELECT_WAIT_MS	Driver loop select() blocking time. Lower = faster wake-up when events arrive mid-block
FMB_TCP_READ_TIMEOUT_MS	150	1–500	MB_READ_TICK	SO_RCVTIMEO for MBAP header read. The biggest latency risk — a partial TCP segment stalls the entire loop
FMB_TCP_SEND_TIMEOUT_MS	100	10–1000	MB_TCP_SEND_TIMEOUT_MS	Writability check + send timeout. Under congestion, this is a per-response stall
FMB_TCP_EVENT_LOOP_TICK_MS	50	5–200	MB_TCP_EVENT_LOOP_TICK_MS	Event loop time budget. Controls how long events block before returning to sockets

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary (manual tests).
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[mo-rige]

I hope to promote the code version for easy testing and use as soon as possible

[alisitsyn]

@mo-rige,

In order to check the issue we need the example code to reproduce issue on both sides with existing environments (base standpoint). As I said the communication timings depend on many aspects and I have different results on my side (wifi for now). If you can, please publish your simplified project which can be used for verification and the sdkconfig file. I will take a look ASAP.

Thanks.

[mo-rige]

@alisitsyn Ok, I will try to streamline the project and achieve its objectives. Please hold on while I upload the complete version of my current project first

[mo-rige]

ESP32S3-M0001.zip
MyProject