chore: standardize tkm unit (#868)

## 🔧 Problem

We have several spelling for the unit ton kilometer : 
- `t⋅km`
- `t*km`
[User
Story](https://www.notion.so/Fix-t-km-t-km-ca6703fc7802460cb6bacdbee4448e0d?pvs=4)

## 🍰 Solution

Standardize to only use `t⋅km`

## 🏝️ How to test

everything should be green

data/textile/activities.json

@@ -1032,7 +1032,7 @@
     "waste": 0,
     "alias": "sea-transport",
     "category": "process",
-    "unit": "t*km"
+    "unit": "t⋅km"
   },
   {
     "id": "247ab69c-daa5-4f81-879f-fac0d33880f2",
@@ -1048,7 +1048,7 @@
     "waste": 0,
     "alias": "air-transport",
     "category": "process",
-    "unit": "t*km"
+    "unit": "t⋅km"
   },
   {
     "id": "f3735a48-3438-4523-8263-5cb101597d82",
@@ -1064,7 +1064,7 @@
     "waste": 0,
     "alias": "train-transport",
     "category": "process",
-    "unit": "t*km"
+    "unit": "t⋅km"
   },
   {
     "id": "463aa3d1-287e-4d4c-a4ed-78d47600a4b1",
@@ -1080,13 +1080,13 @@
     "waste": 0,
     "alias": "road-transport",
     "category": "process",
-    "unit": "t*km"
+    "unit": "t⋅km"
   },
   {
     "id": "6bb6762e-7c0c-4f31-aaef-d0763927a931",
     "name": "Transport en camion non spécifié France (dont parc, utilisation et infrastructure) (50%) [tkm], FR",
     "displayName": "Transport en camion non spécifié France",
-    "unit": "t*km",
+    "unit": "t⋅km",
     "source": "Base Impacts 2.01",
     "sourceId": null,
     "comment": "Ancien identifiant (12/2024): f49b27fa-f22e-c6e1-ab4b-e9f873e2e648.",

public/data/textile/processes.json

@@ -1713,7 +1713,7 @@
     "id": "6bb6762e-7c0c-4f31-aaef-d0763927a931",
     "name": "Transport en camion non spécifié France (dont parc, utilisation et infrastructure) (50%) [tkm], FR",
     "displayName": "Transport en camion non spécifié France",
-    "unit": "t*km",
+    "unit": "t⋅km",
     "source": "Base Impacts 2.01",
     "sourceId": null,
     "comment": "Ancien identifiant (12/2024): f49b27fa-f22e-c6e1-ab4b-e9f873e2e648.",