fix: partial write support and default write endpoint

[alespour]

Proposed Changes

This PR finalizes partial-write support and fixes regression issue with the default API endpoint behavior introduced in PR #365.

• The client defaults to the V2 API endpoint for writes for broad product compatibility. Since the Java client has not been released yet with the PR feat: support partial writes #365 behavior, this change is not breaking.
• V3 API-only options:
  • noSync
  • acceptPartial

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• Tests pass
• Commit messages are conventional

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.29%. Comparing base (e634c9c) to head (1bf2242).

Files with missing lines	Patch %	Lines
...nfluxdb/v3/client/internal/InfluxDBClientImpl.java	77.77%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #388      +/-   ##
==========================================
+ Coverage   88.25%   88.29%   +0.04%     
==========================================
  Files          21       21              
  Lines        1532     1546      +14     
  Branches      277      279       +2     
==========================================
+ Hits         1352     1365      +13     
- Misses         82       83       +1     
  Partials       98       98              

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[Copilot]

Pull request overview

This PR restores V2 write endpoint defaults while preserving V3-only partial-write and noSync support behind useV2Api=false.

Changes:

• Defaults write routing to the V2 API endpoint and updates related tests/expectations.
• Refines V2/V3 method-not-allowed error messages and partial-write error formatting.
• Updates README and changelog language around partial writes and endpoint compatibility.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/main/java/com/influxdb/v3/client/write/WriteOptions.java	Changes default write endpoint selection to V2 and updates validation/docs.
src/main/java/com/influxdb/v3/client/internal/InfluxDBClientImpl.java	Adds endpoint-specific 405 guidance for V2 and V3 writes.
src/main/java/com/influxdb/v3/client/internal/RestClient.java	Adjusts partial-write detail rendering and fallback JSON token formatting.
src/main/java/com/influxdb/v3/client/InfluxDBClient.java	Updates public configuration documentation.
src/main/java/com/influxdb/v3/client/config/ClientConfig.java	Updates write endpoint configuration documentation.
src/test/java/...	Updates and expands tests for defaults, routing, validation, and error formatting.
README.md	Documents default V2 writes and V3-only write options.
CHANGELOG.md	Records partial-write support and V2 default behavior.

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