feat(client): opt-in retry with backoff honoring Retry-After

[Datata1]

Implements plans/refactor/07-retry-support.md (final ticket):

• RetryConfig frozen dataclass (max_retries=0, backoff_factor=0.5, retry_statuses={429,502,503,504}, retry_methods={GET,HEAD,PUT,DELETE}), exported from the top-level package and accepted by CodesphereSDK(retry=...)
• Retry loop in APIHttpClient.request: idempotent methods only by default (POST opt-in via retry_methods), retries on the configured statuses and on httpx timeout/connect errors; delay honors Retry-After (delta-seconds or HTTP-date, past dates clamp to 0) and falls back to exponential backoff with jitter; exhausted retries raise exactly what the non-retry path would (RateLimitError with retry_after populated, TimeoutError, ...); each retry is logged at debug level
• Plain ~40-line loop, no retry dependency reintroduced
• Default max_retries=0 means zero behavior change unless opted in (tested: single request on failure with the default config)
• 17 respx tests: Retry-After honored (429->200 with exactly 2 requests and >=1s sleep), exhaustion, exponential backoff bounds, non-retryable 500, POST gating and opt-in, transport-error retries, SDK wire-through, Retry-After parsing matrix
• README documents RetryConfig

[github-actions]

🛡️ Bandit Security Scan Results

✅ No security issues found by Bandit.

[github-actions]

Pytest Coverage Report

File	Stmts	Miss	Branch	BrPart	Cover	Missing
__init__.py	10	0	0	0	100%
client.py	40	0	6	0	100%
config.py	16	0	0	0	100%
exceptions.py	94	0	38	0	100%
http_client.py	98	3	22	2	96%	124->162, 135->136, 136–137, 162
utils.py	10	2	4	1	79%	9->10, 10–11
core
__init__.py	4	0	0	0	100%
base.py	55	0	2	0	100%
handler.py	59	3	18	0	96%	80–82
operations.py	15	0	0	0	100%
resources
__init__.py	0	0	0	0	100%
resources/metadata
__init__.py	3	0	0	0	100%
operations.py	6	0	0	0	100%
resources.py	13	0	0	0	100%
schemas.py	28	0	0	0	100%
resources/team
__init__.py	5	0	0	0	100%
operations.py	8	0	0	0	100%
resources.py	11	0	0	0	100%
schemas.py	27	0	0	0	100%
resources/team/domain
__init__.py	3	0	0	0	100%
operations.py	11	0	0	0	100%
resources.py	16	0	0	0	100%
schemas.py	55	5	0	0	91%	67, 69, 72, 75–76
resources/team/usage
__init__.py	3	0	0	0	100%
operations.py	4	0	0	0	100%
resources.py	43	2	8	2	92%	99->102, 102, 162->165, 165
schemas.py	70	7	6	5	84%	66->67, 67, 72–73, 76, 84–86
resources/workspace
__init__.py	5	0	0	0	100%
envVars.py	4	0	0	0	100%
operations.py	12	0	0	0	100%
resources.py	16	2	4	2	80%	13->14, 14, 19->20, 20
schemas.py	99	14	6	6	81%	100–101, 103–109, 115–116, 118, 142, 161
resources/workspace/env_vars
__init__.py	3	0	0	0	100%
operations.py	7	0	0	0	100%
resources.py	26	2	12	4	84%	33->35, 35–36, 38->exit
schemas.py	4	0	0	0	100%
resources/workspace/git
__init__.py	3	0	0	0	100%
operations.py	8	0	0	0	100%
resources.py	15	0	4	0	100%
schemas.py	4	0	0	0	100%
resources/workspace/landscape
__init__.py	3	0	0	0	100%
operations.py	12	0	0	0	100%
resources.py	96	7	36	8	89%	28->29, 29, 129->132, 135->138, 161->162, 162–163, 165->160, 168->169, 169, 173–175
schemas.py	290	29	10	4	89%	113–114, 117, 122–123, 126–127, 130, 135–137, 140–141, 144, 251, 258–259, 334–336, 338–340, 342–343, 458–459, 466–467
resources/workspace/logs
__init__.py	3	0	0	0	100%
operations.py	5	0	0	0	100%
resources.py	175	50	60	37	63%	66->68, 68, 97–98, 104, 106–108, 110, 113–114, 117, 120–121, 123–126, 128–129, 132–133, 135–136, 138–139, 141–143, 145–146, 148–152, 154–155, 157–159, 161–166, 179–180, 252–253
schemas.py	22	0	0	0	100%
TOTAL	1519	126	236	71	89%

Test Execution Summary

Tests	Skipped	Failures	Errors	Time
383	0 💤	0 ❌	0 🔥	4.344s ⏱️