Add technical changelog for Minecraft snapshot 25w34b (#25)

Author: Neluxx

1.21.9/25w34b.md

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+pack breaking | Data pack format has been increased to 84.0
+
+pack breaking | Resource pack format has been increased to 66.0
+
+component block-entity | Player profiles in data components and block entities no longer resolve automatically
+
+command | Added `fetchprofile` command for downloading player profiles
+* New command that has been added to fetch the contents of a player profile from Minecraft servers
+* Since the operation might take some time, it works asynchronously
+  * Results will be printed only when operation finishes, but the game will keep running unpaused
+* After successful completion, a message will be printed that lets users copy the contents of a fully resolved `minecraft:profile` component or `/give @s minecraft:player_head` with said component
+* Since the result is not known at the time of execution, this command always returns `1`
+* Syntax:
+  * `fetchprofile name <player name>` - resolves profile by name (case-insensitive)
+  * `fetchprofile id <uuid>` - resolves profile by id
+
+blockstate | Removed `align_items_to_bottom` block state property from Shelf block
+* It has been replaced with an equally named boolean field on the Shelf block entity
+* Shelves created with this property set in the last snapshot will reset back to the default value (`false`)
+
+component | Modified `minecraft:profile`
+* Previously contents of this component would permanently change when profile was resolved, i.e. downloaded from Minecraft service 
+* To avoid issues with this unexpected change, the resolved value is no longer stored and contents of the profile will always remain unchanged 
+* That means this component has now two behaviors:
+  * Static: when it has `properties` field or when both `name` and `id` are present or when both are missing
+    * In this state, profile will always render as-is
+    * If `properties` field is missing, a default skin will be used (selected based on `id`, same as in offline mode)
+    * That means skin will be frozen at the moment of component creation
+    * This option is preferred for decorational uses
+  * Dynamic: when it has either `name` or `id` (but not both)
+    * When an item containing this profile is rendered on the client side, the profile will be resolved to most recent value
+    * This means that this item will always render with current skin of targeted player
+      * Note: if a player changes skin while game is running, change will not be visible unless clients restart
+    * Resolution might happen with a delay, during which item will render with a default skin
+    * Profile name will replace item name only when it's present
+      * Items with just `id` will show default name
+    * Items will dynamic profiles be distinguished from static ones with label in tooltip
+* Items stack based on exact contents, so even if a dynamic component is eventually resolved to the same profile as a static one, they won't stack together
+* Player heads in older maps that have not been loaded in never versions yet will usually be converted to dynamic contents
+
+block-entity | Modified `minecraft:skull`
+* `profile` field has been changed to match `minecraft:profile` component
+  * That means that it also becomes immutable and is resolved only when necessary
+
+text | Bold and italics styles are ignored when drawing sprites