Stop paying for the [TILEDBG] diagnostics when debug logging is off

[CSSFrancis]

_on_view_changed_internal reported the distinct-value counts of the backend's raw native crop and of the sampled tile. Both are np.unique — full sorts — and both were passed as arguments to _TLOG.debug. Lazy %-formatting does not help there: arguments are evaluated before the call, so every pan and zoom paid for them at any log level.

Measured on a 4096² frame. VIEW_OVERFETCH = 2.0 makes the over-fetched crop the whole image at any zoom below 2×, which is where panning actually happens:

	crop	cost
np.unique(raw crop)	4096²	259 ms
np.unique(raw crop)	2048²	65 ms
np.unique(raw crop)	1024²	17 ms
np.unique(tile)	1024²	12 ms

End to end, a pan settle on a 4096² frame:

zoom	before	after
1.1×	378 ms	78 ms
2×	377 ms	81 ms
4×	125 ms	57 ms

The counts are genuinely useful — they catch a backend handing back a downsample instead of native pixels — so they move into _log_fetch_diagnostic behind an isEnabledFor(DEBUG) guard rather than being deleted. _refresh_overview's min/max got the same treatment.

test_tile_diagnostics.py pins the guard rather than the message text, from both sides: no sorting at INFO, the FETCH line still emitted at DEBUG, and the displayed tile byte-identical either way.

Found while chasing slow panning on a 4k in-situ movie in SpyDE. SpyDE needs this released as 0.4.2 before it can bump its anyplotlib>= pin.

Full test_plot2d suite passes (305 + 3 new).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.35%. Comparing base (d4755d4) to head (0ebb0ee).

Files with missing lines	Patch %	Lines
anyplotlib/plot2d/_plot2d.py	66.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
- Coverage   90.41%   90.35%   -0.07%     
==========================================
  Files          39       39              
  Lines        4008     4014       +6     
==========================================
+ Hits         3624     3627       +3     
- Misses        384      387       +3     

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