fix(image): correct block_size validation in PSNRB (and → or)

[xodn348]

Summary

PeakSignalNoiseRatioWithBlockedEffect.__init__ contains a one-character logic error in its input guard: the condition uses and where or is required.

# Before (broken)
if not isinstance(block_size, int) and block_size < 1:

# After (correct)
if not isinstance(block_size, int) or block_size < 1:

With and, the first clause (not isinstance(block_size, int)) evaluates to False for every int, which short-circuits the expression and skips the < 1 check entirely. As a result:

• block_size=0 and block_size=-5 are silently accepted instead of raising ValueError.
• block_size=1.5 is silently accepted (float >= 1 makes the second clause False).
• block_size="foo" raises TypeError from the comparison instead of the intended ValueError.

This PR applies the same or-based guard to the functional peak_signal_noise_ratio_with_blocked_effect, which had no block_size validation at all — an omission noted in the issue thread.

Issue

Fixes #3364

Local verification

# Linter
$ ruff check src/torchmetrics/image/psnrb.py \
             src/torchmetrics/functional/image/psnrb.py \
             tests/unittests/image/test_psnrb.py
All checks passed!

# Tests (9 new + 1 existing)
$ python -m pytest \
    tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_class \
    tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_functional \
    tests/unittests/image/test_psnrb.py::test_error_on_color_images \
    -v

tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_class[0]    PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_class[-5]   PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_class[1.5]  PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_class[foo]  PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_functional[0]    PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_functional[-5]   PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_functional[1.5]  PASSED
tests/unittests/image/test_psnrb.py::test_error_on_invalid_block_size_functional[foo]  PASSED
tests/unittests/image/test_psnrb.py::test_error_on_color_images                        PASSED

9 passed in 2.99s
=== LOCAL_TEST_PASSED ===

Risk

The change only affects the error-path for invalid block_size arguments — no functional computation is touched. Users passing a valid positive integer (block_size >= 1) are unaffected. The only observable behavioral change is that previously-ignored bad inputs now raise ValueError as documented, which is the intended contract. No existing tests regress.

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📚 Documentation preview 📚: https://torchmetrics--3367.org.readthedocs.build/en/3367/