docs(tvix): fix some typos across various documents

Fix some typos found while reading various documents, mostly those
relating to the castore.

Here is a summary of the edits.

- fix broken link between documents in the store and castore directories
- clarify expression in castore's data model document that indicates
  that the *name* of each child node of a directory must be unique
  across all three lists of children
- add missing closing parenthesis in castore's data model document
- replace "how" with "what" in the phrase "unclear how a ... would even
  look like" in castore's why-not-git-trees document
- remove unnecessary articles in castore's blobstore chunking document
- add missing "y" to "optionall" in eval's compilation of bindings
  document

Change-Id: I1997ea91bb4e9c40abcd81e0cde9405968580ba6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11763
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/castore/docs/blobstore-chunking.md

@@ -73,10 +73,10 @@ This means one only needs to the root digest to validate a constructions, and th
 constructions can be sent [separately][bao-spec].
 
 This relieves us from the need of having to encode more granular chunking into
-our data model / identifier upfront, but can make this a mostly a transport/
+our data model / identifier upfront, but can make this mostly a transport/
 storage concern.
 
-For the some more description on the (remote) protocol, check
+For some more description on the (remote) protocol, check
 `./blobstore-protocol.md`.
 
 #### Logical vs. physical chunking