[fix] correct typos / mislabeled examples / table alignment in conditional and date-time function docs

[boluor]

Summary

Fixes 16 small documentation issues across the conditional and date-time function references. Each item below is independent.

conditional-functions

• not-null-or-empty.md / null-or-empty.md — example SQL had an embedded ; inside the SELECT list (not_null_or_empty("");, ... and null_or_empty("");, ...) which makes the statement invalid. The stray ; is removed.
• null-or-empty.md — the Description (both frontmatter and body) said the function returns true when the input is NOT NULL and NOT empty (which is the semantics of not_null_or_empty). Inverted the wording so it correctly describes null_or_empty.
• conditional-functions/overview.md — the short-circuit example's result table had a header row one character shorter than its rulers (rulers were 73 dashes, header was 72). Header and rulers are now the same width.

date-time-functions

• convert-tz.md — result-table header showed CAST(... AS DATEV2) while the query used AS DATE. Header aligned with the query.
• date-sub.md — a stray closing ``` fence sat at the very end of the file with no matching opener. Removed.
• date-trunc.md — the parameters table labelled the first argument \<date_or_time_part>`while the Syntax used``. Unified on ``` to match the syntax (and the convention in sibling docs).
• millisecond-timestamp.md — the 1960-01-01 example showed -315619200000000 (a microsecond magnitude) for a function that returns milliseconds. Corrected to -315619200000.
• maketime.md — the result table included an id column that the query never selects. Removed the id column from the result table (header, separator, and all data rows).
• microsecond-timestamp.md — the 1960-01-01 result-table header row was 1 character shorter than its rulers. Added a trailing space so the table renders square.
• from-iso8601-date.md — inline comments mis-spelled the date-pattern notation as YYY-MMM; corrected to YYYY-Www to match the notation used elsewhere in the doc.
• minute-ceil.md / minute-floor.md (and a few sibling docs that had the same leak: hour-ceil.md, second-ceil.md, second-floor.md) — a Chinese link label [timestamptz的转换] appeared inside English docs; changed to [timestamptz conversion].
• minute-floor.md — a result-table value used .000 while sibling docs use .000000. Aligned to .000000.
• minute-floor.md — a mixed-case MINUTE_floor(...) invocation; corrected to MINUTE_FLOOR(...).
• month-floor.md — the "Period non-positive" example invoked MINUTE_FLOOR and the error message echoed minute_floor (copy-paste from minute-floor.md). Corrected to MONTH_FLOOR / month_floor.
• period-add.md — the Syntax line was PERIOD_ADD(\`, `month`)— second arg missing the angle brackets. Corrected to```.

Test plan

• CI doc build passes
• Spot-check the affected pages render correctly (conditional examples, the short-circuit result table in overview.md, convert-tz result, date-sub end-of-file, date-trunc params, the millisecond-timestamp 1960 example value, maketime result table, microsecond-timestamp 1960 header, ISO-8601 comments, minute/hour/second/month _floor/_ceil examples and link labels, period-add syntax)