Render error caret for the last character of the parsing context

[fudianchn]

Problem

ParsingException.getMessage() renders a caret (^) under the error column, but guards it with column < context.length(). column is 1-indexed (the caret is drawn at position column - 1), so when the error is on the last character — column == context.length() — the caret is dropped (#625).

Fix

-            if (this.column >= 0 && this.column < this.context.length()) {
+            if (this.column >= 0 && this.column <= this.context.length()) {

<= renders the caret for the last character (at position column - 1), while still rejecting positions past the end.

Verification

The caret logic in isolation (the exact branch from getMessage):

column == context.length() (last char, 1-indexed):
  OLD (<):  caret rendered? false   ← bug
  NEW (<=): caret rendered? true    ← caret line "    ^" under the last char
  column=3 (mid):    OLD/NEW both render  ← no regression
  column=6 (past end): NEW no caret        ← still rejected

Added ParsingExceptionTest (caretRenderedForLastColumn / caretNotRenderedBeyondContext) — the repo's Gradle build was too heavy to run locally, but the caret logic is verified above and the test codifies it for CI.

Closes #625