Align UCUM byte unit conversions with the specification table

[thswlsqls]

Fixes #8751

Description

• Spec unit table: TiBy -> tebibytes, kBy -> kilobytes. The referencing section is Status: Stable; the conversion is a MUST.
• We had TiBy -> tibibytes, and only upper case KBy, so kBy went out unconverted.
• KBy is not in the table (K is kelvin in UCUM) but stays as an alias, so existing users keep kilobytes.
• Metric names change: ..._tibibytes becomes ..._tebibytes. The existing test asserted tibibytes, so it is corrected too.
• No compatibility switch: Stop converting unit "1" to "ratio" in Prometheus exporter #8252 changed this table for the far more common unit 1 with no switch or deprecation, and this artifact is alpha.
• Upstream prometheus/otlptranslator fixed both entries but kept the old spellings in an opt-out legacyUnitMap; happy to do the same here.

Testing done

• PrometheusUnitsHelperTest: the TiBy case now expects tebibytes, plus a new kBy -> kilobytes case. Both fail before the fix (tibibytes, kBy) and pass after.
• ./gradlew :exporters:prometheus:check — 203 tests plus testJpms pass.
• No apidiff change: alpha artifact, package-private class.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.29%. Comparing base (e2efec5) to head (d6996ab).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8752   +/-   ##
=========================================
  Coverage     91.29%   91.29%           
  Complexity    10498    10498           
=========================================
  Files          1006     1006           
  Lines         28338    28339    +1     
  Branches       3581     3581           
=========================================
+ Hits          25870    25872    +2     
  Misses         1675     1675           
+ Partials        793      792    -1     

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Pull request dashboard status

Waiting on maintainers · refreshed 2026-09-03 17:27 UTC

Merge when ready.

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