fix: unaligned 64-bit atomic panic on 32-bit platforms in telemetry buffers

[Kirill-INQ]

Description

On 32-bit platforms (GOARCH=arm, GOARCH=386), every event capture panics with unaligned 64-bit atomic operation: the offered/dropped counters of RingBuffer and BucketedBuffer are plain int64 fields in the middle of the struct, and the compiler only guarantees them 4-byte alignment there, while 64-bit sync/atomic operations require 8-byte alignment (see the "Bugs" section of the sync/atomic docs). Since Client.CaptureEvent routes through RingBuffer.Offer by default, the SDK is effectively unusable on 32-bit ARM (e.g. Raspberry Pi) unless DisableTelemetryBuffer is set.

This PR replaces the counters with atomic.Int64, whose alignment is guaranteed by the runtime regardless of field position, so future struct refactorings can't reintroduce the panic.

Verified with the existing test suite on a 32-bit target — before the change it reproduces the panic natively:

$ GOARCH=386 go test ./internal/telemetry/
panic: unaligned 64-bit atomic operation
  ...
  github.com/getsentry/sentry-go/internal/telemetry.(*RingBuffer[...]).Offer(...)
      internal/telemetry/ring_buffer.go:75
FAIL

after the change:

$ GOARCH=386 go test ./internal/telemetry/
ok      github.com/getsentry/sentry-go/internal/telemetry

go test ./..., go vet, gofmt are clean on amd64 as well.

Issues

• resolves: panic: unaligned 64-bit atomic operation on 32-bit ARM (GOARCH=arm) — telemetry RingBuffer counters #1354

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.46%. Comparing base (1ce3436) to head (b08daf9).
⚠️ Report is 149 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/telemetry/bucketed_buffer.go	71.42%	2 Missing ⚠️
internal/telemetry/ring_buffer.go	83.33%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (1ce3436) and HEAD (b08daf9). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (1ce3436)	HEAD (b08daf9)
	9	1

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1355      +/-   ##
==========================================
- Coverage   86.04%   78.46%   -7.59%     
==========================================
  Files          62       87      +25     
  Lines        6090     8032    +1942     
==========================================
+ Hits         5240     6302    +1062     
- Misses        635     1431     +796     
- Partials      215      299      +84     

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