fix(server): return read item errors for invalid ranges

[gijzelaerr]

Summary:

• return 0x0A for reads from unregistered server areas
• return 0x05 for reads outside or crossing registered memory
• preserve item-level errors for single and multi-item reads
• add integration regressions and a changelog entry
• remove stale S7CommPlus references from CI and API documentation after its extraction

Validation:

• 1379 passed, 49 skipped
• pre-commit passed
• documentation built with warnings treated as errors
• source distribution and wheel built successfully

Closes #894.

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