fix: hourly canvas chart date labels

[djbarnwal]

Fixes temporal X-axis labels for canvas charts using hourly grain over wider time ranges.

Previously, hourly axes used %H:%M for every tick. For ranges like 14 days, Vega-Lite often chooses midnight ticks, which made labels repeat as 00:00. This updates hourly temporal axis labeling so midnight ticks render as dates and other ticks still render as times.

• Adds a temporal axis labelExpr for hourly grain formatting.
• Shows day-boundary ticks as %b %d.
• Keeps non-midnight ticks as %H:%M.

Examples

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[nishantmonu51]

👍