fix(monitor_priority): compare the iterated monitor in the unmapped scan

[IvanTopGaming]

Problem

With monitor_priority in use, monitors not listed get a workspace base
that is too high, so their workspace range is wrong.

My setup — one physical monitor and one headless output created at runtime:

local hs = require("hyprsplit")
hs.config({ num_workspaces = 10 })
hs.monitor_priority({ "DP-1" })

Expected DP-1 → 1-10, HEADLESS-1 → 11-20.
Actual HEADLESS-1 → 21-30.

Cause

In MonitorRange:new, the scan that collects unmapped monitors compares the
outer monitor (the one whose range is being computed) instead of m,
the monitor currently being iterated:

for _, m in ipairs(hl.get_monitors()) do
    ...
    for _, monitor_selector in ipairs(hyprsplit.monitor_priority_list) do
        if
            monitor.name == monitor_selector          -- always the same monitor
            or monitor.description == monitor_selector
        then

While computing the range for an unlisted monitor, that condition is false for
every m, so no monitor is ever marked as mapped. Monitors already present
in monitor_priority_list end up in unmappedMonitors as well, which shifts
the index of the genuinely unmapped ones by the size of the priority list.

For the example above unmappedMonitors becomes {DP-1, HEADLESS-1}, giving
HEADLESS-1 index 1, hence base = 1 + #monitor_priority_list = 2 → 21-30.

Fix

Compare the iterated monitor.

Verification

Extracting the function's logic and running it standalone against two mock
monitors, {"DP-1"} as the priority list:

before: DP-1=1-10  HEADLESS-1=21-30
after:  DP-1=1-10  HEADLESS-1=11-20

Confirmed on Hyprland 0.56.2: after the change the headless output is assigned
11-20 and hs.dsp.focus({ workspace = 1 }) on it lands on workspace 11.

Unrelated note

If base is never assigned it stays -1, which yields min = -9, max = 0.
The identity check if monitor == m a few lines below relies on the two values
being the same object. That held in my testing, so I left it alone — but if
monitor can ever arrive from a different source than hl.get_monitors(),
a name comparison plus a guard on base == -1 might be worth adding.