…es#52111)

## Context

`TerminalBounds::num_lines()` uses `floor(height / line_height)` to
compute the terminal grid row count. When the height is derived from `N
* line_height` (as it is for inline/embedded terminals in the Agent
Panel), IEEE 754 float32 arithmetic can produce `N - epsilon` instead of
`N`, causing `floor()` to return `N - 1`. This makes the terminal grid
one row too small, leaving the first line of output in invisible
scrollback (since `display_offset = 0`). The same issue applies to
`num_columns()`.

The fix adds a small tolerance (`0.01`) before flooring, which absorbs
float precision errors without affecting genuine fractional results.

Closes zed-industries#51609

## How to Review

Small PR — focus on the tolerance value (`0.01`) in `num_lines()` and
`num_columns()` in `crates/terminal/src/terminal.rs`. The two new tests
(`test_num_lines_float_precision`, `test_num_columns_float_precision`)
verify the fix across 1,000+ float combinations that previously
triggered the bug.

## Self-Review Checklist

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed the first line of terminal output sometimes missing in Agent
Panel terminal blocks.

This PR fixes test flakiness introduced in
#52111

The flakiness was because the test was using its own RNG, rather than
using gpui's built-in support for consistently-seeded RNGs in tests. The
fix was just to adjust the test to use the same logic for computing row
and column count as was introduced in the above PR.

Release Notes:

- N/A