fix(markdown): escape pipes in code spans inside table cells

[tomsideguide]

A row is split into cells before any inline is parsed, so a pipe is syntax inside a code span too. Plain text, styled text and URLs already escaped it in a cell; code spans did not, because push_code_span was the one emitter that never received the context it was rendering into.

Both cell code paths route through it, the inline code run and a <pre> block in a cell, so passing the context fixes both.

Before, on a two-column table:

| `a | b` | bitwise or |

The delimiter row declares two columns and the body row emits three, so a GFM renderer drops bitwise or and tears the code span in half. After:

| `a \| b` | bitwise or |

Closes #84

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Summary by cubic

Escapes pipes in Markdown code spans inside table cells so they no longer split columns. Previously, a pipe in a cell code span acted as a delimiter; now it renders as |, and an existing | renders as \| to preserve the escape. Code outside tables is unchanged.

• Pass InlineContext into push_code_span and escape only for InlineContext::TableCell.
• Route both inline code and cell <pre> code through push_code_span; add tests for "a | b" and pre-escaped "a | b".
• Move and rename the escaper to escape.rs as escape_cell_code_span; restore the backtick_fence doc comment.

^{Written for commit 85d3606. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 3 files

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Fix all with cubic | Re-trigger cubic</sub>