pdms: use evict API for TSO primary transfer

[bufferflies]

What problem does this PR solve?

TSO service may have multiple keyspace groups, each with its own primary. The old transfer API only handles a single group's primary. This PR uses the new evict API (introduced in tikv/pd#10968) that transfers all keyspace group primaries from the TSO node at once.

What is changed and how does it work?

• Add pdMSPrimaryEvictPrefix = "api/v1/primary/evict" constant
• In TransferPrimary, for TSO service, try the evict API first (POST /tso/api/v1/primary/evict). If it succeeds, return. On failure (old PD without evict support), fall back to the old transfer API (POST /tso/api/v1/primary/transfer).
• Non-TSO services (router, scheduler) continue to use the transfer API directly.

Code changes

• Has Go code change

Tests

• Unit test (existing tests pass)

Related changes

Related to tikv/pd#10968

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.54%. Comparing base (a16b2e8) to head (2b19560).
⚠️ Report is 72 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7022      +/-   ##
==========================================
+ Coverage   57.19%   57.54%   +0.34%     
==========================================
  Files         259      262       +3     
  Lines       33233    38240    +5007     
==========================================
+ Hits        19008    22004    +2996     
- Misses      12291    14156    +1865     
- Partials     1934     2080     +146     

Flag	Coverage Δ
unittest	57.54% <0.00%> (+0.34%)	⬆️

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[liubog2008]

Add a feature gate to change current api call. Hence this api is not available for all pd versions.

[liubog2008]

add a new feature gate for this incompatible change

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[LGTM Timeline notifier]

Timeline:

• 2026-08-07 03:56:12.924222828 +0000 UTC m=+2759558.960317885: ✖️🔁 reset by liubog2008.