Fix #249: preserve whitespace around stripped block-level elements

[apoorvdarshan]

Summary

Fixes #249. When a block-level element such as <div> is stripped (via strip=[...]) or excluded from a convert=[...] whitelist, the whitespace separating it from its neighbouring text was dropped, running the words together.

from markdownify import markdownify as md

md('<span>Ignored <div>Still ignored</div> tag.</span>', strip=['div'])
# before: 'IgnoredStill ignoredtag.'
# after:  'Ignored Still ignored tag.'

Root cause

process_text() removes whitespace immediately outside a block-level sibling (should_remove_whitespace_outside). That is correct for a converted block, which emits its own \n\n separation. But a stripped block is emitted inline, so stripping the surrounding whitespace leaves no separator at all.

Fix

Only treat a block-level sibling as a whitespace boundary when it is actually being converted. A new helper _removes_adjacent_whitespace() combines the existing block-level check with should_convert_tag(), so a stripped (inline-rendered) sibling now keeps the separating whitespace. Converted blocks are unaffected.

The reporter's own workaround (overriding convert_div to pad with spaces) left a trailing space; this approach avoids that because the stripped element's own leading/trailing whitespace is still normalised — only the inter-element separator is preserved.

Verification

• Added test_strip_block_element_preserves_surrounding_whitespace covering both strip=['div'] and convert=['span']. It fails on develop and passes with this change.
• Full suite: 84 passed (was 83).
• flake8 --ignore=E501,W503 markdownify tests clean.
• Manually confirmed no change for converted blocks (<p>a</p><p>b</p> → a\n\nb) and for stripped inline elements (strip=['b'] still keeps spaces).

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Disclosure: prepared with AI assistance; reviewed and verified locally against the test suite.