Add CHANGELOG for 1.5.4

[philippjfr]

This release primarily focuses on improving the ESM components including fixes for serialization of parameter values, improvements for compiling bundles, and building custom layouts. Additionally this release includes the new DatetimeSlider, adds a copy button to codeblocks in Markdown panes and starts adding better support for Polars. Many thanks and a warm welcome to our new contributor @MP-MaximilianLattka as well as our maintainer team, including @hoxbro, @thuydotm, @ahuang11, @MarcSkovMadsen and @philippjfr.

Enhancements

• Add DatetimeSlider widget (#7374)
• Improve Jupyter preview error handling (#7434)
• Add copy button to Markdown codeblocks (#7451)
• Various improvements for writing ESM components (#7462)
• Log authorization callback errors (#7463)
• Support polars in pn.cache (#7472)
• Improve and document hold utility (#7474)
• Improve how panel compile collects bundles (#7477)

Bug fixes

• Fix issues detecting changed property values during serialization (#7432)
• Ensure ESM compilation correctly detects file extension (#7446)
• Ensure parameter overrides are applied to ESM components (#7452)
• Ensure component Children parameter correctly resolves when multiple types are defined (#7454)
• Fix issues using Jupyter Preview with notifications enabled (#7466)
• Ensure HTML/Markdown streaming does not freeze during rapid updates (#7480)
• Ensure Plotly sizes correctly on initial render (#7483)