Logger constants refactored, format argument added, better formatting of failed (non) equality assertions (#9315)

# Description
I have (hopefully) simplified the `log.nu` internal structure and added
customizable log format for all `log` commands

# User-Facing Changes
- [x] Replaced constants with env records for: 
    - ansi (newly added)
    - log level
    - prefix
    - short prefix
- [x] Added `format` argument to all log commands
- [x] Assertions for (not) equality (equal, not equal, greater,
lesser...) now put left and right values inside `'` quotes, so the
assertions for strings are more meaningful
- [x] Documented the %-formatting of log messages

# Tests + Formatting
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---------

Co-authored-by: amtoine <stevan.antoine@gmail.com>

crates/nu-std/std/assert.nu

@@ -143,7 +143,7 @@ export def equal [left: any, right: any, message?: string] {
     main ($left == $right) $message --error-label {
         start: (metadata $left).span.start
         end: (metadata $right).span.end
-        text: $"They are not equal. Left = ($left). Right = ($right)."
+        text: $"They are not equal. Left = '($left)'. Right = '($right)'."
     }
 }
 
@@ -160,7 +160,7 @@ export def "not equal" [left: any, right: any, message?: string] {
     main ($left != $right) $message --error-label {
         start: (metadata $left).span.start
         end: (metadata $right).span.end
-        text: $"They both are ($left)."
+        text: $"They both are '($left)'."
     }
 }
 
@@ -177,7 +177,7 @@ export def "less or equal" [left: any, right: any, message?: string] {
     main ($left <= $right) $message --error-label {
         start: (metadata $left).span.start
         end: (metadata $right).span.end
-        text: $"Left: ($left), Right: ($right)"
+        text: $"Left: '($left)', Right: '($right)'"
     }
 }
 
@@ -193,7 +193,7 @@ export def less [left: any, right: any, message?: string] {
     main ($left < $right) $message --error-label {
         start: (metadata $left).span.start
         end: (metadata $right).span.end
-        text: $"Left: ($left), Right: ($right)"
+        text: $"Left: '($left)', Right: '($right)'"
     }
 }
 
@@ -209,7 +209,7 @@ export def greater [left: any, right: any, message?: string] {
     main ($left > $right) $message --error-label {
         start: (metadata $left).span.start
         end: (metadata $right).span.end
-        text: $"Left: ($left), Right: ($right)"
+        text: $"Left: '($left)', Right: '($right)'"
     }
 }
 
@@ -226,7 +226,7 @@ export def "greater or equal" [left: any, right: any, message?: string] {
     main ($left >= $right) $message --error-label {
         start: (metadata $left).span.start
         end: (metadata $right).span.end
-        text: $"Left: ($left), Right: ($right)"
+        text: $"Left: '($left)', Right: '($right)'"
     }
 }