fix: DH-18279: fix one click titles

[jnumainville]

Example from DH-18279

import deephaven.plot.express as dx
from deephaven.plot.figure import Figure
from deephaven.plot.selectable_dataset import one_click

stocks = dx.data.stocks()

one_click = Figure().plot_xy(series_name="Stock Prices", t=one_click(stocks, ["Sym"]), x="Timestamp", y="Price").show()

Title now updates as the input filter is updated

PR Overview

A fix to ensure one click titles update correctly by adjusting title padding and triggering layout update events properly.

• Updated the setTitle method to recalculate margins based on title content.
• Added a test to verify that the title update event is fired exactly once.

Reviewed Changes

File	Description
packages/chart/src/FigureChartModel.test.ts	Added test to ensure title update events are triggered correctly.
packages/chart/src/FigureChartModel.ts	Modified setTitle to adjust margins and trigger layout update events.

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

packages/chart/src/FigureChartModel.ts:629

• The title update event appears to be fired twice in the setTitle method, which may lead to unintended side effects and fails the test expectation. Consider removing the duplicate call so that the event is fired only once.

this.fireLayoutUpdated({ title: this.layout.title });

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.80%. Comparing base (d44370b) to head (764c89f).

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2381    +/-   ##
========================================
  Coverage   46.79%   46.80%            
========================================
  Files         710      710            
  Lines       39234    39235     +1     
  Branches     9976     9791   -185     
========================================
+ Hits        18361    18365     +4     
- Misses      20819    20859    +40     
+ Partials       54       11    -43     

Flag	Coverage Δ
unit	46.80% <100.00%> (+<0.01%)	⬆️

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