Stylize chat components

[ahuang11]

Allows properly targeting and styling parts of the ChatMessage

import panel as pn

pn.extension()

pn.chat.ChatMessage(
    "Testing",
    show_activity_dot=True,
    stylesheets=[
        """                    
    .message {
        background-color: tan;
        font-size: 24px;
        font-family: "Courier New";
    }
    .avatar {
        background-color: red;
        border-radius: 5%;
    }
    .right {
        background-color: grey;
    }
    .center {
        background-color: pink;
    }
    .left {
        background-color: yellow;
    }
    .header {
        background-color: green;
    }
    .footer {
        background-color: blue;
    }
    .name {
        background-color: orange;
    }
    .timestamp {
        background-color: purple;
    }
    .activity-dot {
        background-color: black;
    }
    .reaction-icons {
        background-color: white;
    }
    .copy-icon {
        background-color: gold;
    }
"""
    ],
).show()

I did notice that parts of the chat message alignment isn't ideal (e.g. left doesn't fill all the way squarely).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (723768e) 82.65% compared to head (b2ea056) 84.12%.
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6346      +/-   ##
==========================================
+ Coverage   82.65%   84.12%   +1.46%     
==========================================
  Files         305      305              
  Lines       45468    45499      +31     
==========================================
+ Hits        37580    38274     +694     
+ Misses       7888     7225     -663     

Flag	Coverage Δ
ui-tests	40.81% <11.76%> (+2.20%)	⬆️
unitexamples-tests	71.63% <100.00%> (-0.01%)	⬇️

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[philippjfr]

Some test failures, otherwise looks good.