Fix Context Overload in Read File Tool

Problem

The read_file tool could attempt to read files that exceed the available context window, causing API failures and poor user experience.

Solution

Added preemptive context validation that dynamically calculates available space and applies intelligent file size limits.

Changes

New contextValidator module:

• Calculates remaining context space based on current token usage
• Reads files incrementally in batches to count actual tokens
• Returns safe maximum line count with 25% safety buffer
  Enhanced readFileTool:
• Validates file size before reading when partial reads are off
• Provides inline instructions to model when files are truncated to use line_range syntax
• Respects user-specified limits when provided

Fix

Turn off partial reads, and open Roo-Code-Evals/javascript/lodash. Ask the following prompt from this task: https://app.roocode.com/share/fa7affcc-611d-46ff-89a4-d741d8593b2a

Remaining concerns:

• The model is now shown the tool line_range if a file cannot fit in context. This means that if it reads a very large file, then normal sized files, in theory it could continue to use the line_range tool to do unnecessary partial reads even when partial reads are deactivated.
• The 25% safety buffer is not guaranteed robust but empirically seems fine
• Fails if you try reading the E.coli document which is one big line
• Still fails if you try and force Roo to read the entirety of the bible. This seems to be a problem of inefficient context condensing.

Fixes #7744