feat: Use forward and reverse tokenization

We enable the "reverse" tokenization mode, which allow to search both in
forward and backward directions on tokens.
The forward mode allows to search from left to right, while the reverse
mode allows the opposite. For example, with the word "example", you can
search "exam" in forward mode, and "ample" in reverse.

We measured a 15-20% memory impact on enabling the reverse tokenization,
compared to the forward mode.
The "full" mode, allowing searching on all combinations, including in
the middle of the word, comes with ~70% memory increase. So, we decided
to to not enable it for now, as the cost/benefit ratio of such feature
is unclear.

The memory cost of enabling the reverse mode seems however reasonable.

packages/cozy-dataproxy-lib/src/search/SearchEngine.ts

@@ -180,7 +180,7 @@ export class SearchEngine {
     const fieldsToIndex = SEARCH_SCHEMA[doctype]
 
     const flexsearchIndex = new FlexSearch.Document<CozyDoc, true>({
-      tokenize: 'forward',
+      tokenize: 'reverse', // See https://github.com/nextapps-de/flexsearch?tab=readme-ov-file#tokenizer
       encode: getSearchEncoder(),
       // @ts-expect-error minlength is not described by Flexsearch types but exists
       minlength: 2,