docs: fix typos in comments and documentation

[Avicennasis]

Summary

Fixes 30 typos in doc comments across 7 files. No functional changes -- comments only, with the single exception of one error-message string noted below.

The one substantive fix

• events.go -- GetOldestEvent's doc comment read "will fetch the latest event for a issue", a copy-paste of GetLatestEvent's comment directly above it. The function body requests issues/%s/events/oldest, so the comment documented the wrong behaviour. Changed to "will fetch the oldest event for an issue".

Grammar / spelling (the rest)

• issue.go (12 lines): a issue -> an issue x11; a issues tag -> an issue's tag; happend -> happened
• client.go (3 lines): a auth -> an auth x2; a optional -> an optional; a empty -> an empty
• project.go (2 lines): fetchs -> fetches x2; a organization -> an organization
• events.go (3 lines): a event -> an event; a issue -> an issue x2 (plus the latest/oldest fix above)
• organization.go (2 lines): quote -> quota; There is not way -> There is no way
• stat.go (1 line): tetting -> getting
• datatype/stacktrace.go (2 lines): a exception -> an exception x2; olds -> holds

Notes for reviewers

• The a empty -> an empty change in client.go is inside the error text fmt.Errorf("Endpoint can not be a empty string"). It is the only change outside a comment. I grepped the repo -- no test asserts on that string.
• Deliberately not changed: the exported field SymboleAddr in datatype/stacktrace.go and its json:"symboleAddr,omitempty" tag. It is misspelled, but it is an exported identifier and the tag must keep matching Sentry's own wire field name, so renaming it would be a breaking API change rather than a typo fix.
• The same misspellings appear in files outside this change (team.go, userfeedback.go, datatype/message.go, and some _test.go files). I kept this PR to the files listed above to stay reviewable; happy to extend it if you would prefer a single sweep.
• No formatting changes: gofmt -l reports the same six files before and after this commit (pre-existing drift under datatype/), and I left them alone.

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