test: add comprehensive unit tests for Template::Provider

[toddr-bot]

What

85 unit test assertions for Template::Provider, the template loading/compiling/caching layer.

Why

Provider is one of the most complex modules in TT — it handles file loading, INCLUDE_PATH resolution, LRU caching with a doubly-linked list, compiled template management, and Unicode BOM detection. None of these internals had dedicated unit test coverage; existing t/provider.t only exercises it indirectly through the template engine.

How

Direct method-level tests using Test::More with File::Temp for isolated filesystem fixtures. Coverage spans:

• Constructor: option defaults, CACHE_SIZE normalization, INCLUDE_PATH coercion, DELIMITER, ENCODING, DEFAULT, STAT_TTL
• paths(): static lists, blank filtering, coderef generators, object generators, error propagation, MAX_DIRS limit
• _template_content/_template_modified/_modified: file reads, error paths, stat checks
• _load(): scalar refs, file handles, file paths, aliases, TOLERANT mode
• fetch(): absolute/relative/include-path routing, TOLERANT downgrades, DEFAULT fallback, scalar refs, file handles
• load(): raw content retrieval (INSERT semantics) with same path-type routing
• store/_store: cache insertion, LRU eviction at SIZE limit, head/tail pointer integrity
• Negative cache: NOTFOUND population on miss, STAT_TTL expiry
• _compiled_filename/_compiled_is_current: COMPILE_EXT/DIR path construction, mtime comparison, result caching
• COMPILE_DIR: on-disk compiled file creation
• _decode_unicode: UTF-8 BOM detection, ENCODING fallback, already-decoded passthrough
• DESTROY: linked list circular reference cleanup
• RELATIVE_PATH regex: pattern matching verification

Testing

perl -Ilib t/provider_methods.t — 85/85 pass. Full make test passes with no regressions.

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Quality Report

Changes: 1 file changed, 987 insertions(+)

Code scan: 1 issue(s) found

• t/provider_methods.t:0 — 987 lines added

Tests: passed (OK)

Branch hygiene: clean

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