feat: add file exporter implementation

[herin049]

Description

Adds support for the OTLP JSON File exporter as outlined in OTel spec: https://opentelemetry.io/docs/specs/otel/protocol/file-exporter/

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

uv run tox -e py314-test-opentelemetry-exporter-otlp-json-file

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[ocelotl]

Lookiing good! Left some comments but in general I am ok ✌️

[pmcollins]

Nice addition. I ran this code locally to see the output and got {"resource": {}} JSON lines, whereas the spec examples embed this in a little bit of additional structure: {"resourceSpans": [{"resource": {}}]} {"resourceMetrics": [{"resource": {}}]} {"resourceLogs": [{"resource": {}}]}.

[herin049]

https://opentelemetry.io/docs/specs/otel/protocol/file-exporter/

@pmcollins Good catch, I should be writing a single line for each TracesData object not each ResourceSpans object. Will update the PR shortly.

[herin049]

@pmcollins Updated.

[Copilot]

Pull request overview

Adds a new opentelemetry-exporter-otlp-json-file distribution implementing the OTLP JSON File exporter spec. Provides FileSpanExporter, FileMetricExporter, and FileLogExporter that write newline-delimited OTLP JSON either to stdout (default), a provided text stream, or a file path. The shared writing logic and metric temporality/aggregation env handling live in a _internal.py module mirroring the existing proto-common metrics encoder helpers.

Changes:

• New package exporter/opentelemetry-exporter-otlp-json-file with FileExporter core (lock-protected JSON Lines writer), three signal exporters, and entry points (otlp_json_file).
• Wiring into workspace config (pyproject.toml, uv.lock, eachdist.ini, tox.ini) and CI matrices (test.yml adds Ubuntu+Windows jobs for 3.10–3.14, 3.14t, PyPy 3.10; lint.yml adds a lint job).
• Comprehensive tests for formatting, env-driven temporality/aggregation, per-signal export/shutdown/path/stream behavior, and round-trip equivalence with encode_*().to_dict().

Reviewed changes

Copilot reviewed 22 out of 24 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
exporter/opentelemetry-exporter-otlp-json-file/src/.../_internal.py	Generic FileExporter writing JSON Lines under a lock; metric temporality/aggregation env helpers duplicated from proto-common mixin.
exporter/.../trace_exporter.py, metric_exporter.py, _log_exporter.py	Per-signal exporters wrapping FileExporter and mapping its bool result to SDK enums.
exporter/.../tests/test_*.py	Unit tests for formatting, env helpers, export/shutdown/path/stream paths, and encoder round-trip equivalence.
exporter/.../pyproject.toml, README.rst, LICENSE, version/__init__.py, test-requirements.txt	Package metadata, entry points, dependencies, license, and test deps.
pyproject.toml, uv.lock, eachdist.ini, tox.ini	Workspace registration, deps, and tox envs/commands for the new package.
.github/workflows/test.yml, lint.yml	CI test jobs across Python versions on Ubuntu/Windows and a lint job.
.changelog/5207.added	Changelog entry.
exporter/opentelemetry-exporter-otlp-json-common/README.rst	Tightens README wording (drops empty "used by" list).

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