Sort numeric text columns by value in the cluster tables

[adityasingh2400]

Sorting the Cluster View by the channel column ch orders channels as text rather than as numbers, so a single-digit channel lands in the wrong place relative to a two-digit one. Ascending order comes out as 1, 10, 2, 21, 3 instead of 1, 2, 3, 10, 21.

The cause is that ch holds a channel label, and TemplateController.get_best_channel_label formats it with f'{ch}', so the value stored in the table is a string. _TableProxyModel.lessThan compares raw values with <, which for two strings is a character by character comparison. Every column whose values arrive as text has the same problem, not just ch.

This adds _text_sort_key, used by lessThan when either side is a string. Entries that parse as numbers sort first and in numeric order, and the remaining entries keep their existing string ordering, so a mixed column such as a label column stays predictable. Non-string values keep the previous exact comparison path, so integer and float columns are unaffected.

Verified headlessly against a table holding the channel labels 2, 10, 1, 21, 3. Before the change the ascending order was ['1', '10', '2', '21', '3'], after it is ['1', '2', '3', '10', '21']. Two regression tests were added to phy/gui/tests/test_widgets.py, one for a purely numeric text column and one for a column mixing numbers and free text. Both fail on master and pass with the fix. make lint, make format-check, and pytest phy/gui/tests/test_widgets.py phy/cluster/tests/test_supervisor.py all pass, 106 tests.

Fixes #1405