docs: describe the clickhouse fork pin as it is

[catinspace-au]

Two doc corrections, no code.

• CLICKHOUSE-EXT.md said the fork is pinned to an immutable tag. Cargo.toml:300 pins rev 6f9acd96, the tip of hyperi-port/06d-tcp-tls-new, and none of the fork's 30 tags points at it. The fork repo is archived, so the branch can no longer move and the rev stays reachable. It also means retiring the patch (Pre-GA bug sweep: the clickhouse patch #133) is the only way a client fix lands.
• INSERT-FORMATS.md: "ten rows written for UInt8 are 90 bytes" only adds up with the UInt64 id column (9 bytes a row). It now says ten (id UInt64, v UInt8) rows, read by an (id UInt64, v UInt16) table as nine rows.