Properly handling entity meanings in datastore.

…/python-docs-samples#1241)

Protobuf handles the base64 encoding for you, and so the content was being base64 encoded twice.

…1241)

* fix: don't retry if error or error_description is not string

* chore: fix flaky sample test

* chore: update sys test cred

Thank you for opening a Pull Request! Before submitting your PR, there
are a few things you can do to make sure it goes smoothly:
- [x] Make sure to open an issue as a
[bug/issue](https://github.com/googleapis/python-bigtable/issues/new/choose)
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Fixes #1239

PR created by the Librarian CLI to initialize a release. Merging this PR
will auto trigger a release.

Librarian Version: v0.7.0
Language Image:
us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/python-librarian-generator@sha256:b8058df4c45e9a6e07f6b4d65b458d0d059241dd34c814f151c8bf6b89211209
<details><summary>google-cloud-bigtable: 2.35.0</summary>

##
[2.35.0](googleapis/python-bigtable@v2.34.0...v2.35.0)
(2025-12-16)

### Features

* add basic interceptor to client (#1206)
([6561cfac](googleapis/python-bigtable@6561cfac))

* Add encodings for STRUCT and the Timestamp type
([72dfdc44](googleapis/python-bigtable@72dfdc44))

* add PeerInfo proto in Bigtable API
([72dfdc44](googleapis/python-bigtable@72dfdc44))

* Add Type API updates needed to support structured keys in materialized
views
([72dfdc44](googleapis/python-bigtable@72dfdc44))

* support mTLS certificates when available (#1249)
([ca20219c](googleapis/python-bigtable@ca20219c))

### Bug Fixes

* re-export AddToCell for consistency (#1241)
([2a5baf11](googleapis/python-bigtable@2a5baf11))

* async client uses fixed grace period (#1236)
([544db1cd](googleapis/python-bigtable@544db1cd))

* Deprecate credentials_file argument
([72dfdc44](googleapis/python-bigtable@72dfdc44))

* Add ReadRows/SampleRowKeys bindings for materialized views
([72dfdc44](googleapis/python-bigtable@72dfdc44))

* retry cancelled errors (#1235)
([e3fd5d86](googleapis/python-bigtable@e3fd5d86))

</details>

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

* observability: add updated span events + traace more methods

This change carves out parts of PR #1241 in smaller pieces to
ease with smaller reviews.
This change adds more span events, updates important spans
to make them more distinct like changing:

"CloudSpanner.ReadWriteTransaction" to more direct and more
pointed spans like:
* CloudSpanner.Transaction.execute_streaming_sql

Also added important spans:
* CloudSpanner.Database.run_in_transaction
* CloudSpanner.Session.run_in_transaction

* all: update review comments + show type for BeginTransaction + remove prints

* Remove requested span event "Using Transaction"

* Move attempts into try block

* Transform Session.run_in_transaction retry exceptions into events

* More comprehensive test for events and attributes for pool.get

* Add test guards against Python3.7 for which OpenTelemetry is unavailable + address test feedback

* Remove span event per mutation in favour of future TODO

Referencing issue #1269, this update removes adding
a span event per mutation, in favour of a future TODO.

* Sort system-test.test_transaction_abort_then_retry_spans spans by create time

* Delint tests