fix(tsp): check write_termination before loading large scripts

[AdarshJ173]

Summary

Closes #500

TSP instruments enforce a 1000-character maximum per VISA write when write_termination is not configured. load_script() previously assembled the entire loadscript … endscript block into a single write string with no length check, silently truncating or erroring on any script body that pushes the total over 1000 characters.

Root Cause

# BEFORE — single write, no length guard
self.write(f"loadscript {script_name}\n{script_body}\nendscript")

The reporter's repro (print("123456…" with 967+ chars) produces a 1000+ char write. Without write_termination, the instrument receives the truncated bytes and returns an unexpected error; the caller gets no indication of why.

Fix

_TSP_WRITE_MAX_CHARS: int = 1000   # new module-level constant

Three-path logic in load_script(), replacing the single write:

Condition	Behaviour
len(full_cmd) <= 1000	Single write — identical to before, zero behaviour change for small scripts
len(full_cmd) > 1000 AND write_termination falsy	Raise ValueError with a clear message explaining the limit and how to fix it
len(full_cmd) > 1000 AND write_termination set	3-phase multi-write: loadscript {name} → body in ≤1000-char chunks → endscript

Multi-write protocol (phase 3 path)

# Phase 1: open context
self.write(f"loadscript {script_name}")
# Phase 2: stream body in chunks
for chunk_start in range(0, len(script_body), _TSP_WRITE_MAX_CHARS):
    self.write(script_body[chunk_start : chunk_start + _TSP_WRITE_MAX_CHARS])
# Phase 3: close context
self.write("endscript")

This matches the TSP multi-write protocol described in Keithley's TSP documentation.

Error message (path 2)

ValueError: Script 'overrun' requires 1023 characters to load, which exceeds the TSP
per-write limit of 1000 characters. TSP instruments cannot receive scripts larger than
this limit without a write_termination character configured on the VISA resource.
Set write_termination before loading large scripts, e.g.:
device.visa_resource.write_termination = '\n'

Impact

• Small scripts (≤ 1000 chars total): no behaviour change whatsoever.
• Large scripts without write_termination: was silent truncation / confusing instrument error → now immediate ValueError with actionable message.
• Large scripts with write_termination: was broken → now works correctly via chunked write.

Changes

• src/tm_devices/driver_mixins/device_control/tsp_control.py
  • New module constant _TSP_WRITE_MAX_CHARS = 1000
  • load_script() length check and three-path write logic
  • Updated docstring with Raises section and Note about the 1000-char limit

No public API changes, no new dependencies, no schema migrations.

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[nfelt14]

This needs to be a class constant, so subclasses can overwrite it if necessary