feat: support partial writes

[alespour]

Proposed Changes

Adds partial-write support with structured error details in InfluxDBPartialWriteException, including per-line LineNumber, ErrorMessage, and OriginalLine so callers can decide whether to drop/retry/fix specific lines in a ba
tch.

This also aligns write routing with the rollout contract:

• Default write endpoint is now /api/v3/write_lp
• AcceptPartial defaults to true (server default behavior)
• accept_partial=false is sent only when partial writes are explicitly disabled
• New compatibility option UseV2Api routes writes to /api/v2/write for Clustered/v2-compatible backends

Configuration surfaces now include:

• Write option: AcceptPartial, UseV2Api
• Client config / connection string keys: writeAcceptPartial, writeUseV2Api
• Environment variables: INFLUX_WRITE_ACCEPT_PARTIAL, INFLUX_WRITE_USE_V2_API

Validation:

• UseV2Api=true with NoSync=true is rejected before request dispatch.

See Partial writes in InfluxDB documentation.

Example:

try
{
    await client.WriteRecordAsync(lp); // AcceptPartial=true by default
}
catch (InfluxDBPartialWriteException e)
{
    foreach (var lineErr in e.LineErrors)
    {
        Console.WriteLine(
            $"line {lineErr.LineNumber} failed: {lineErr.ErrorMessage} ({lineErr.OriginalLine})");
    }
}
catch (InfluxDBApiException e)
{
    Console.WriteLine(e.Message);
}

Optional v2 compatibility mode:

using var v2Client = new InfluxDBClient(new ClientConfig
{
    Host = host,
    Token = token,
    Database = database,
    WriteOptions = new WriteOptions
    {
        UseV2Api = true
    }
});

await v2Client.WriteRecordAsync(lp);

Checklist

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

[Copilot]

Pull request overview

Adds structured partial-write error support and updates write routing defaults to align with InfluxDB v3 behavior, while providing an opt-in v2 compatibility route.

Changes:

• Introduces InfluxDBPartialWriteException with per-line error details and updates REST error parsing to surface it for v3 partial-write responses.
• Changes default write endpoint to /api/v3/write_lp, adds WriteOptions.AcceptPartial (default true) and WriteOptions.UseV2Api for routing to /api/v2/write, plus config/env/connection-string support.
• Updates unit/integration tests and documentation/changelog to reflect the new defaults and options.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
README.md	Documents partial writes and v2 compatibility mode configuration.
Client/Internal/RestClient.cs	Switches error parsing to System.Text.Json and throws InfluxDBPartialWriteException when line errors are present.
Client/InfluxDBPartialWriteException.cs	Adds a new exception type carrying structured line-level errors.
Client/InfluxDBClient.cs	Routes writes to v3 by default; adds v2 routing option and query params for no_sync / accept_partial.
Client/Config/WriteOptions.cs	Adds AcceptPartial and UseV2Api plus validation for incompatible option combinations.
Client/Config/ClientConfig.cs	Adds connection string and env var parsing for new write options.
Client/Client.csproj	Adds System.Text.Json dependency for netstandard targets.
Client.Test/Internal/RestClientTest.cs	Expands tests to cover typed/untyped partial-write parsing and the new exception type.
Client.Test/InfluxDBClientWriteTest.cs	Updates expected write paths/query params for new v3 default and v2 compatibility mode.
Client.Test/InfluxDBClientHttpsTest.cs	Updates expected write endpoint to v3.
Client.Test/InfluxDBApiExceptionTest.cs	Updates expected write endpoint to v3.
Client.Test/Config/ClientConfigTest.cs	Adds coverage for new connection string/env config keys.
Client.Test.Integration/WriteTest.cs	Minor refactor for exception typing consistency.
CHANGELOG.md	Notes breaking default write routing + partial write support.

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