Apply render_cell plugin hook to primary key columns

[westurner]

This update modifies the table view to execute the render_cell plugin hook against simple (single) primary key (or "Link") columns. Instead of always generating a default HTML anchor link pointing to the row view, Datasette now checks if any plugin returns a custom display value. If a custom rendering is provided, it is used; otherwise, it safely falls back to the default <a href="..."> behavior.

Key Changes & Optimizations:

• Feature: Executes render_cell hooks for simple primary keys in display_columns_and_rows, safely resolving pk_value from the row.
• Performance: Pre-computes has_single_pk, pk_index, and has_render_cell_hooks outside of the O(N) row loop to eliminate redundant operations.
• Performance: Completely skips hook evaluation if no plugins are registered to listen to render_cell.
• Refactor: Streamlines row cell appending by using an inline A if A is not None else B fallback, which prevents duplicate dictionary initializations and safely handles intentional empty strings ("") returned by plugins.
• Compatibility: Passes pks=pks_for_display to the hook call to satisfy upstream API requirements.

Assisted By: Gemini 3.1 Pro

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📚 Documentation preview 📚: https://datasette--2652.org.readthedocs.build/en/2652/

[westurner]

From https://github.com/pulp for example:

All contributors must indicate in the commit message of their contribution if they used AI to create them and the contributor is fully responsible for the content that they submit.

This can be a label such as Assisted By: or Generated by: based on what was used.

So I added "Assisted By:". I would say this one was more of a pair coding with LLMs than a vibe coding. I ran the tests a number of times locally. I'm not sure why I have 15 local test failures before and after this PR. Does the Actions build run the tests with coverage?