Fix /metrics page displays true, false instead of 0, 1

[pohlm01]

According to the OpenMetrics specification, boolean values must be encoded as 0 and 1.
I encontered this bug while using Prometheus to scrape the metrics, which produced the following error line and resulted in no values being reported for any metric.

ts=2025-02-21T09:55:03.007Z caller=scrape.go:1307 level=debug component="scrape manager" scrape_pool=local_ptp target=http://localhost:1337/metrics msg="Append failed" err="strconv.ParseFloat: parsing \"false\": invalid syntax"

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.58%. Comparing base (758aa8b) to head (e3ec31d).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
statime-linux/src/metrics/format.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #617   +/-   ##
=======================================
  Coverage   61.58%   61.58%           
=======================================
  Files          62       62           
  Lines        8415     8414    -1     
=======================================
  Hits         5182     5182           
+ Misses       3233     3232    -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.